Substantive equality in part-time work. The evolving protection of the Part-time Work Directive

Abstract

This article examines how the protection against discrimination based on part-time work has evolved towards a model of substantive equality in the case law of the Court of Justice of the European Union (CJEU). The focus is on the non-discrimination clause in the Part-time Work Directive and conditions of pay, and Norwegian law is used to illustrate the issues and the impact on national law. The analysis starts by highlighting important aspects of the non-discrimination clause; the fundamental question of what constitutes different treatment, the requirements to justify it and the role of the principle of pro rata temporis. From there, the developments in case law in cases concerning conditions of pay are further scrutinised. The analysis explores two diverging approaches to what constitutes different treatment, developed in case law on the principle of equal pay for male and female workers and highlight how they align with the concepts of direct and indirect discrimination. The article further dwells on how this broad model of equality is confirmed and clarified in recent case law on the Part-time Work Directive, by applying the principle of pro rata temporis. The analysis of justification requirements also explores the problematic nature of conditions of pay that appear to be equal but have adverse effects in part-time work. Although these developments bring the protection against discrimination based on part-time work in line with protection against discrimination on other grounds in EU law, they challenge national regulations on overtime pay and other remuneration supplements, as in Norwegian law.

1. Part-time work, equality and conditions of pay

A part-time worker is an employee whose normal hours of work are less than the normal hours of work of a comparable full-time worker. ² The agreed hours of work thus mark an inherent difference. The general principle of equality in EU law implies that comparable situations must not be treated differently unless objectively justified. One manifestation is the principle of non-discrimination on the grounds of part-time work. ³ But what does equality mean in this context? To answer this, two legal questions must be addressed: What constitutes unequal treatment based on part-time work, and how can differences in treatment be justified?

This article discusses these two questions based on the Part-time Work Directive (97/81/EC). The Directive's non-discrimination clause stipulates that part-time workers shall not be treated less favourably than comparable full-time workers in respect of employment conditions, unless this can be justified on objective grounds. ⁴ The Directive also recognises that – when appropriate – a principle of pro rata temporis shall apply, which means that a condition of work is set proportionally, according to the hours of work.

The article focuses on conditions of pay, more precisely time-related remuneration. ⁵ Pay is typically calculated with reference to time, for example hours of work. Payment in money is a divisible benefit that can be calculated proportionally. It is accepted to set pay for part-time employees pro rata temporis based on their actual working hours. ⁶ However, salary schemes often include different elements, such as a basic salary and additional remuneration. The complexity generates uncertainty around what constitutes different treatment and how to compare part-time and full-time employees: Is it the full, overall pay or each condition or aspect of remuneration that should be ‘equal’? And does the principle of non-discrimination only target inequalities in respect of the level of pay related to hours of work, or can it also address other disadvantages or adverse effects of the relevant salary scheme?

There are important developments on these issues in the case law of the Court of Justice of the European Union (CJEU). In two recent rulings – case C-660/20 Lufthansa CityLine and case C-184/22 KfH Kuratorium – the Court has clarified the approach(es) to what constitutes different treatment based on part-time work concerning pay. ⁷ The rulings also provide important guidance on how this type of different treatment can be justified. These developments have the potential to significantly impact national law in many European countries.

In the following, I will discuss the developments on what constitutes different treatment (Section 3) and how it can be justified (Section 4). Norwegian law will be used to illustrate the issues and the impact on national law. ⁸ As a basis for the analysis, I will first present the national (Norwegian) context and highlight some important aspects of the Directive's non-discrimination clause (Section 2). I conclude with some reflections on the developments (Section 5).

2. A national context and the Part-time Work Directive's non-discrimination clause

In Norway, as in the other Nordic countries, there is a strong tradition not to regulate levels of pay in statutory law, but rather to leave it to the social partners to set rates of pay in collective agreements or in the individual employment contract. One important exception is the Working Environment Act (WEA) ⁹ Section 10-6 (11), which provides for a right to overtime pay. For overtime work, a supplement of at least 40% shall be paid in addition to the pay for equivalent work during normal working hours. Overtime work is defined as work exceeding the statutory limits for normal working hours, which are set irrespective of the agreed working hours. ¹⁰ The threshold for the right to overtime pay is thus uniform and applies to both part-time and full-time employees. A majority of workers are covered by collective agreements that often contain specific rules on overtime pay and other additional remuneration. ¹¹ Many of these agreements, both in the public and private sectors, have similar thresholds; the right to overtime supplement is contingent on work exceeding the normal hours of full-time employees.

The Part-time Work Directive is included in the EEA Agreement and was implemented in the WEA in 2005. ¹² The regulations on overtime pay were not considered problematic in light of the non-discrimination clause, but this was not discussed in any depth. The preparatory works simply state that ‘those employees who work part-time or have reduced working hours, as is the case today, do not have the right to overtime pay until their working hours exceed the [statutory limits for] normal working hours’. ¹³

The Directive's non-discrimination clause is rooted in the principle of equal pay and other protections against discrimination on the grounds of sex. ¹⁴ As women are more likely than men to work part-time, different treatment of part-time employees may have adverse effects on women and constitute indirect discrimination on the grounds of sex. Therefore, the issue of discrimination of part-time workers in conditions of pay has been addressed in case law on the principle of equal pay, cf. the current TFEU Article 157. ¹⁵ Here, the CJEU has first considered whether there is a difference in treatment based on part-time work, and has then examined whether this has an adverse effect on women. The legal relevance of examining different treatment based on part-time work in EU law therefore precedes the adoption of the Part-time Work Directive. Nonetheless, the Directive was a significant step towards broader protection against discrimination based on part-time work, as it is independent and applies irrespective of how women are affected.

The principle of non-discrimination in Clause 4 reads:

In respect of employment conditions, part-time workers shall not be treated in a less favourable manner than comparable full-time workers solely because they work part time unless different treatment is justified on objective grounds.

Where appropriate, the principle of pro rata temporis shall apply.(…)

This rather short and simple wording contrasts with other anti-discrimination Directives. The Directive does not specify what constitutes different treatment, more precisely whether both direct and indirect forms of discrimination are prohibited. Furthermore, the requirements to justify different treatment are not elaborated, beyond the reference to ‘objective grounds’. Other anti-discrimination Directives explicitly define and prohibit both forms of different treatment, and the justification requirements are more specific. ¹⁶ The two aspects are closely interrelated. Other anti-discrimination Directives specify that indirect discrimination can be justified by a legitimate aim, if the means for achieving that aim are appropriate and necessary, while the requirements to justify direct forms of discrimination in employment are significantly stricter. ¹⁷ The lack of differentiated justification requirements in the Part-time Work Directive may therefore explain why the non-discrimination clause is not explicit on direct and indirect forms of discrimination. ¹⁸

Nevertheless, at the time of its implementation into Norwegian law, the simple wording led to ambiguity regarding whether both direct and indirect discrimination were prohibited, and whether the justification requirements were parallel to those of other anti-discrimination Directives. ¹⁹ The legislator eventually chose to apply a ‘similar concept of discrimination’ as in other areas of discrimination law, and explicitly prohibited both direct and indirect forms and specified the same, general justification requirements. ²⁰

A prohibition of direct discrimination targets less favourable treatment based on specific characteristics. It operationalises a model of formal equality and embodies the idea that individuals are equal irrespective of characteristics such as sex and ethnicity, and should be treated the same way. ²¹ A prohibition of indirect discrimination, however, addresses apparently neutral provisions or practices that would put persons with certain characteristics at a particular disadvantage without a sufficient justification. It is linked to a model of substantive equality. In this model, group characteristics are seen as a relevant part of the individual's real situation that must be taken into account in order to achieve equality. ²² Equality thus depends on how regulations or decisions affect people with the relevant characteristic.

The CJEU has never explicitly referred to the concepts of direct and indirect discrimination when interpreting the Part-time Work Directive's non-discrimination clause. The Court's approach to different treatment based on part-time work can still reveal whether both forms are prohibited, and case law indicates that indirect forms of discrimination can be covered. The non-discrimination clause has been applied in cases of different treatment based on neutral criteria, based on the negative impact on a group consisting mainly of part-time workers. ²³ Nevertheless, the following analysis will show that uncertainty has lingered in the context of pay and remuneration for hours of work, due to diverging approaches in case law on the principle of equal pay. ²⁴

The requirements to justify different treatment based on part-time work are more resolved, at least on a general level. The Court has clarified that ‘objective grounds’ refer to the general requirements of legitimate aim, appropriateness and necessity. ²⁵ There has, however, been a lack of specific guidance on how to apply the justification test within the context of pay and part-time work. ²⁶

The principle of pro rata temporis is another distinctive aspect of the Directive's non-discrimination clause, compared to most other anti-discrimination Directives. ²⁷ The Directive stipulates that the principle ‘shall apply’, but only ‘when appropriate’, and the latter condition is rather vague. Pay is a divisible benefit and can be calculated proportionally based on working hours, but it is still not fully clear how this relates to the question of different treatment. ²⁸ The principle of pro rata temporis is often presented as a clarification of what is permissible; an employment condition set proportionally – when appropriate – does not violate the non-discrimination clause. ²⁹ For example, in Norwegian preparatory works and literature, the principle has been presented as a specification of ‘objective grounds’. ³⁰ However, the principle may also imply that adjusting an employment condition proportionally can be required in order to avoid violating the non-discrimination clause. If so, the principle of pro rata temporis elucidates the meaning of different treatment and reflects that conditions that formally are the same for part-time and full-time workers may be discriminatory. Consequently, there is potentially a close link between the applying the principle of pro rata temporis and a non-discrimination clause that prohibits indirect forms of discrimination.

Before examining the developments in case law, two initial points must be highlighted. Firstly, as a manifestation of the general principle of equality, the non-discrimination clause cannot be interpreted restrictively. This has been underscored repeatedly by the CJEU when interpreting other anti-discrimination Directives as well as the Part-time Work Directive. ³¹

Secondly, the non-discrimination clause must be interpreted in light of the purpose of the Directive. The explicit purpose to eliminate discrimination of part-time workers aligns with the aim to improve the quality of part-time work. ³² However, the Directive also seeks ‘to facilitate the development of part-time work on a voluntary basis and to contribute to the flexible organization of working time in a manner which takes into account the needs of employers and workers’. ³³ The CJEU has characterised the latter as an aim ‘to promote part-time work’. ³⁴ This signals consideration of the individual needs that can motivate a person to choose part-time work. As the article will show, this consideration is now influencing the CJEU's assessments of what constitutes different treatment and what is required to justify it.

3. What is different treatment?

3.1. A development in CJEU case law

The CJEU has adopted two distinct approaches to identify different treatment based on part-time work concerning pay, with the principle of equal pay as the legal basis. In an initial case, the key question was whether the part-time employee received the same overall pay for the same number of hours worked. However, in another case, the assessment focused on the burden imposed on part-time employees by specific conditions of pay. In subsequent cases, the CJEU has employed both approaches, without explaining or discussing how they are related.

Some seem to regard the two approaches as conflicting and perhaps even mutually exclusive, implying that the assessment of different treatment must rely on either one or the other. ³⁵ However, I propose an alternative perspective: Has the CJEU rather developed a broader and nuanced understanding of unequal treatment in conditions of pay based on part-time work, by extending protection against discrimination to target not only direct, but also indirect, discrimination? If so, the two approaches are complementary and may well coexist.

In the following sections, I will examine case law by first presenting the two approaches in more detail (Section 3.2), then discussing the relationship between them (Section 3.3), before concluding (Section 3.4).

3.2. Two distinct approaches

3.2.1. Case C-399/92 Helmig: same overall pay for the same number of hours worked

The first case, C-399/92 Helmig, concerned collectively bargained provisions on pay that are familiar from a Norwegian perspective. ³⁶ Overtime supplements for both part-time and full-time employees were conditioned on work exceeding the same hourly threshold; the standard, full-time working hours. Helmig and other part-time employees claimed that this constituted different treatment (with an adverse effect on women) in violation of the principle of equal pay, arguing that the overtime supplement should apply once they exceeded their agreed working hours. ³⁷ The CJEU however held that ‘[t]here is unequal treatment wherever the overall pay of full-time employees is higher than that of part-time employees for the same number of hours worked on the basis of an employment relationship’. ³⁸ As the uniform threshold ensured the same overall pay for the same number of hours worked, the Court concluded that there was no different treatment of part-time employees.

The same overall pay for the same number of hours worked was thus deemed ‘equal’. This approach implies a non-discrimination clause that only targets actual disparities in pay based on part-time work. It ensures that overall pay is the same for both part-time and full-time employees based on the number of hours they actually work. However, this approach does not consider the characteristics of part-time work, namely, a lower number of agreed working hours. Consequently, the approach fails to account for the real situation of part-time employees and how conditions of pay that appear to be equal may have adverse effects on them. ³⁹ The reasoning thus implies a non-discrimination clause that only addresses direct forms of discrimination and corresponds with a model of formal equality.

The assumption that the right to overtime pay in Norwegian law was unaffected by the Part-time Work Directive, was probably based on Helmig, although the case was not referenced. On the other hand, the explicit prohibition of both direct and indirect discrimination based on part-time work in national law should have called for more than one approach. And – at the time of implementation – CJEU had already given another ruling, based on a distinctively different approach.

3.2.2. Case C-285/02 Elsner-Lakeberg: the burden imposed on part-time employees

The second case, C-285/02 Elsner-Lakeberg, concerned rather unusual conditions of pay. ⁴⁰ The regulations at issue provided an overtime supplement for work exceeding the agreed working hours, but only when the extra work surpassed three hours per month. While the supplement was linked to the agreed working hours, the ‘extra threshold’ was the same irrespective of part-time work. The question was whether this constituted different treatment of part-time employees (with an adverse effect on women) in violation of the principle of equal pay. ⁴¹ At the time of the ruling, the Part-time Work Directive had been adopted, but it was not invoked in the case.

The CJEU did not refer to Helmig. Conversely, the Court distanced itself from an overall assessment and held that ‘an effective review [of the principle of equal pay] is assured only if that principle applies to each aspect of remuneration …, excluding any general overall assessment of all the consideration …’. ⁴² Therefore, the supplement for additional hours was examined separately. Although the threshold ‘may appear to be equal’, the Court found it to constitute different treatment. The unpaid hours imposed a ‘greater burden’ on part-time employees than for full-time employees in light of their lower agreed working hours, as the extra hours were not reduced proportionately. ⁴³

Elsner-Lakeberg thus focuses on each aspect of renumeration and demonstrates that what appears to be equal can constitute different treatment based on part-time work. In this reasoning, ‘equality’ depends on the effects of neutral condition of pay for persons in part-time work. Although the principle of pro rata temporis is not mentioned, the ruling illustrates that conditions of pay may have to be adjusted pro rata temporis to avoid treating part-time employees differently. This approach takes the characteristics of part-time work into account. It acknowledges that part-time work affects the situation of workers and may invoke adjusting measures to ensure equality. This aligns with a prohibition of indirect discrimination and supports a model of substantive equality.

It is worth noting that the Helmig approach could have provided a basis for finding different treatment in this case. However, assessing whether part-time employees received the same overall pay for the same number of hours worked, would have been rather complex. In the circumstances of this case (involving 2.5 hours of additional work), the part-time employee was paid less than a full-time employee for the same number of hours worked. With more extensive additional working hours, the total pay of the part-time employee would gradually ‘catch up’ to that of a full-time employee. Furthermore, the Helmig approach would have had a greater impact on the salary scheme. Guaranteeing the same pay for the same number of hours worked would in some cases require fully disregarding the provision of unpaid hours, while a proportional reduction was sufficient according to Elsner-Lakeberg. Therefore, Elsner-Lakeberg also implies that applying the principle of pro rata temporis may be more appropriate to ensure equality than focusing on actual disparities in pay.

Elsner-Lakeberg was not referenced when the Directive was implemented in Norwegian law. ⁴⁴ The ruling may have been considered less relevant in the national context, due to the unusual facts of the case. The reasoning nevertheless challenges the view that the right to overtime pay in Norwegian law is unproblematic. Still, until recently, nobody seems to have reflected on the possible implications of Elsner-Lakeberg in Norwegian law. ⁴⁵

3.3. The relationship between the two approaches

3.3.1. A return to Helmig in case C-300/06 Voß?

When considering two different approaches, a pressing question is how they relate to one another: Are they contradictory, or are they complementary, potentially reflecting a development in case law towards protection of both direct and indirect forms of discrimination based on part-time work as regards conditions of pay? As indicated earlier, the CJEU has never explicitly addressed this. The rulings following Helmig and Elsner-Lakeberg still contribute to a clearer understanding.

The third case was Case C-300/06 Voß. ⁴⁶ The regulations at issue set very unusual conditions of pay. Employees received overtime pay for work exceeding their agreed hours, but at a lower hourly rate than their regular pay. Consequently, the reduced rate applied after a lower number of working hours for part-time employees than for full-time employees. The question was whether this was different treatment based on part-time work (with an adverse effect on women), in violation of the principle of equal pay. ⁴⁷ The protection of the Part-time Work Directive was not explicitly invoked.

Here, the CJEU seemed aware of the two approaches. It first referred to the assessment in Helmig, and then, ‘by contrast’, to Elsner-Lakeberg. ⁴⁸ The approach in Helmig was applied when examining the case, without an explicit reasoning. The Court simply pointed out that a part-time employee working beyond the agreed working hours would receive less pay than a full-time employee working the same number of hours. It emphasised that this disparity was a result of the lower overtime rate and concluded that this gave rise to a difference in treatment based on part-time work. ⁴⁹

Some, including Norwegian authorities, have attached great importance to the Court's application of the Helmig approach. It has been argued that the Court in Voß thereby ‘distanced itself from the method … in Elsner-Lakeberg’ and limited the relevance of this approach when it chose and ‘confirmed’ the Helmig approach. ⁵⁰

In my view, this interpretation is strained. In Voß, the Helmig approach provided a clear basis to find different treatment. As the lower rate applied for work exceeding the agreed working hours, less favourable treatment was formally and inextricably linked to part-time work – a direct form of discrimination. The ruling therefore in my opinion only confirms the obvious; a direct form of discrimination is sufficient to establish that discrimination has occurred. The ruling does not conflict with a protection against discrimination that encompass both direct and indirect forms. If direct discrimination can be found, there is no need to examine indirect discrimination.

3.3.2. Clarification in case C-660/20 Lufthansa CityLine

The tension between the two approaches was further intensified in the fourth case, C-660/20 Lufthansa CityLine. ⁵¹ This case concerned a collective agreement for pilots that provided for a remuneration supplement when flying duty hours exceeded monthly thresholds, which applied to both full-time and part-time employees. ⁵² A part-time pilot claimed additional pay on the grounds that the threshold should be reduced proportionally, this time with the Part-Time Work Directive as the legal basis. The case clearly demonstrates that the Court relies on case law concerning the principle of equal pay when assessing what constitutes different treatment based on part-time work under the Directive.

Therefore, the case provided an opportunity to clarify the relationship between the two approaches. Uniform thresholds for additional remuneration ensure equal pay for the same number of hours, and the facts were parallel to those in Helmig. ⁵³ If the sole approach were that of Helmig, no discrimination could be found. However, the pilot's argument was based on the Elsner-Lakeberg approach, and the referring court phrased the question as a choice between the two approaches: ⁵⁴

‘1. Does a national statutory provision treat part-time workers in a less favourable manner than comparable full-time workers within the meaning of Clause 4.1 of the Framework Agreement … if it permits additional remuneration for part-time and full-time workers to be uniformly contingent on the same number of working hours having been exceeded, and therefore allows account to be taken of the overall remuneration, and not of the component of the remuneration that comprises the additional remuneration?’

The Commission and several EU/EEA Member States got involved and submitted observations in the case. ⁵⁵ The Advocate General concluded that the Helmig approach should be applied and generally is decisive, unless the structure of the salary is ‘too complex to be judicially reviewed’. ⁵⁶ However, a premise for this analysis seems to be that one approach must prevail. ⁵⁷ As explained above, the two approaches may well coexist, reflecting a non-discrimination clause that prohibits both direct and indirect discrimination.

The CJEU did not concur with the analysis of the Advocate General, nor did the Court provide a thorough analysis of what constitutes different treatment. The Elsner-Lakeberg approach was simply applied, without reference being made to Helmig or Voß. The Court noted that when the entitlement to additional remuneration is conditional on work exceeding uniform thresholds, the consequence is that ‘part-time pilots do not reach the trigger thresholds required to be entitled to additional remuneration, or are much less likely to do so than full-time pilots’. ⁵⁸ Furthermore, the Court emphasised that although the thresholds ‘appear to be equal’, they represented a longer flight service time for part-time pilots than for full-time pilots in relation to their working time, and, ‘consequently, a greater burden’. ⁵⁹ The burden was elaborated as a ‘negative impact for part-time pilots in terms of the relationship between the service provided and the consideration for it’. The Court concluded that this was a difference in treatment compared to full-time pilots. ⁶⁰

The reasoning aligns with a prohibition of indirect discrimination. It examines whether apparently neutral conditions place individuals in part-time work at a particular disadvantage. Although not explicitly stated, it is implied that conditions of pay may have to be adjusted pro rata temporis to avoid violating the non-discrimination clause.

The ruling in Lufthansa CityLine provides important clarifications. Elsner-Lakeberg was not substantially limited by Voß and clearly has relevance in other factual contexts. Consequently, Helmig cannot be the sole approach to different treatment in conditions of pay based on part-time work. However, this does not preclude a continuous relevance for the approach in Helmig (and Voß); disparities in pay for the same number of hours worked may still constitute different treatment.

From a Norwegian perspective, the ruling in Lufthansa CityLine may have dramatic implications. The reasoning clearly implies that the setting of uniform thresholds for overtime supplements in Norwegian law constitutes different treatment of part-time employees. Some doubts may still linger due to the specific facts of the case, as it did not involve overtime pay in a strict sense. Therefore, there was considerable anticipation surrounding the Court's ruling in a similar case shortly thereafter, which presented facts fully parallel to Norwegian law.

3.3.3. Confirmation in case C-184/22 Kfh Kuratorium

The fifth and final case, C-184/22 KfH Kuratorium, ⁶¹ concerned a collective agreement stipulating a right to overtime supplement for work exceeding the normal weekly working hours for full-time employees – a full parallel to Norwegian law. Two part-time nurses claimed overtime supplement for work exceeding their agreed working hours, arguing that the uniform threshold constituted discrimination. One of the questions raised was whether this was different treatment according to the Part-time Work Directive.

As in Lufthansa CityLine, the Court applied the Elsner-Lakeberg approach and found a difference in treatment based on part-time work. The reasoning is essentially the same: Even if the remuneration for overtime ‘appears to be equal’, it has an adverse effect for part-time employees. They will not – or are much less likely to – reach the required number of hours of work, and the uniform threshold represents a greater burden for them than for full-time employees. ⁶² The Court explicitly stated that not reducing the threshold pro rata temporis constitutes different treatment based on part-time work. ⁶³

The ruling confirms the relevance of the Elsner-Lakeberg approach in yet another factual context. The reasoning shows more clearly that the principle of pro rata temporis is applied to address indirect forms of discrimination. The ruling eliminates any doubt regarding the assessment of Norwegian law: Uniform thresholds for overtime supplements in national law clearly impose a greater burden on part-time employees and thus constitute (an indirect form of) different treatment.

3.4. Protection against direct and indirect discrimination based on part-time work

The CJEU has developed and expanded the understanding of what constitutes different treatment based on part-time work in respect of conditions of pay. The initial focus was on actual disparities in pay, comparing the overall pay of full-time and part-time employees based on the number of hours worked. The approach was anchored in the principle of equal pay between male and female workers and served as a first step in the examination of discrimination based on sex. A supplementary approach later emerged, examining the effects or burdens of apparently neutral conditions of pay for part-time employees. This approach too, was anchored in the principle of equal pay, but – interestingly – emerged only after the adoption of the Part-time work Directive and the recognition of part-time work as an independent discrimination ground. More recently, this development has been confirmed and clarified in case law explicitly based on the Directive's non-discrimination clause.

The latter approach recognises that the real situation for employees in part-time differs from that of those in full-time work. Emphasising the characteristics of part-time work also recognises the individual needs that can explain the choice to do part-time work. While the Court has not reasoned using the terms direct and indirect discrimination, the reasoning aligns with these legal concepts. In other words, the protection against discrimination based on part-time work in respect of conditions of pay has evolved from prohibiting only direct discrimination to also encompassing indirect forms of discrimination, by applying the principle of pro rata temporis.

This development may have far-reaching implications in national law, as illustrated by Norwegian law. The regulation of pay in both statutory law and collective agreements constitutes different treatment, prohibited by the Part-Time Work Directive, unless it can be justified on objective grounds, which will be examined next.

4. How can different treatment be justified?

4.1. Introduction

When national regulations in respect of pay are found to constitute different treatment based on part-time work, a pressing question is whether this can be justified on objective grounds in accordance with the Directive. As explained above, this requires that different treatment can be objectively justified by a legitimate aim, and that the means of achieving that aim are appropriate and necessary. ⁶⁴ In Norwegian law, these requirements explicitly apply to part-time work as a protected ground. ⁶⁵

Both Lufthansa CityLine and KfH Kuratorium raised the question of whether different treatment in the form of uniform thresholds for remuneration supplements can be justified. ⁶⁶ These seem to be the only rulings where the CJEU has examined the justification requirements for this specific type of different treatment under the Directive. In neither case did the Court find sufficient justification. In the following, I will elaborate on the guidance from these rulings and the implications for national law, for the assessment of legitimate aim (Section 4.2), and appropriateness and necessity (Section 4.3).

4.2. Legitimate aim?

It has already been established by case law that a difference in treatment cannot be justified solely on the basis that the difference is provided for by a general norm, such as a statutory act or a collective agreement. Further, an abstract assessment of the purpose is not sufficient. The assessment must be made in the specific context, where the difference in treatment must respond to a genuine need to be legitimate. ⁶⁷ If the aim is not explicitly stated, it must be assessed based on the general scheme of the regulations in question. ⁶⁸

In Lufthansa CityLine, the aim of the remuneration supplement was to compensate for a particular workload and deter airlines from mobilising pilots excessively. ⁶⁹ This is a clear parallel to the explicit aim of the statutory right to overtime pay in Norwegian law, which is to ensure compensation and ‘serve as a limiting factor’ to ‘prevent extensive use of overtime’. ⁷⁰ The compensatory aim is based on the view that overtime is a burden for the employee, and limiting the use of overtime is closely linked to the purpose of protection the health, safety and welfare of employees. ⁷¹

In KfH Kuratorium, the aim of the overtime supplement was slightly different: On the one hand, deterring employers from requiring workers to work overtime in excess of the individually agreed hours, and, on the other hand, preventing full-time employees from being treated less favourably than part-time employees. ⁷²

The latter aim was rejected by the CJEU as based on a premise that ‘is incorrect’. ⁷³ This was a logical consequence of the approach to different treatment: When the Court had found that the threshold must be reduced pro rata temporis to be considered equal, this could not simultaneously constitute different treatment (of full-time employees). The Court also emphasised – based on previous case law – that in so far as national regulations are underpinned by economic considerations, rigorous personnel management is a budgetary consideration that cannot justify discrimination. ⁷⁴ These clarifications are particularly relevant for collectively bargained provisions. The economic and practical considerations that often influence the negotiated solutions will, in principle, not be sufficient, and an aim of ‘equal’ treatment of full-time employees is not a legitimate aim.

The Court has not found an aim of compensating for a particular workload and deterring an employer from assigning excessive extra work – parallel to the statutory right to overtime pay in Norwegian law – to be illegitimate in principle. However, in line with previous case law, the Court has set strict requirements for evidence that this aim responds to a genuine need. In order to ensure this, the difference in treatment must be justified by ‘the presence of precise and specific factors’ in the specific context ‘on the basis of objective and transparent criteria’. ⁷⁵ In Lufthansa CityLine, the Court referred to the lack of ‘objectively determined values or scientific knowledge, or … general experimental data’, for example relating to the effects of monthly flying hours, and concluded that it ‘therefore [did not] appear to be any objective and transparent criteria’ to ensure that the trigger thresholds responded to a genuine need. ⁷⁶ This implies that the difference in treatment must have a scientific basis or be supported by objective data, and that the documentation must be rather specific to the rule in question.

Consequently, when assessing whether the statutory right to overtime pay in Norwegian law has a legitimate aim, a key issue is whether there is sufficient documentation to support the uniform threshold for overtime supplement. The statutory regulations on working time are generally grounded on research on factors affecting health, safety and welfare, and the preparatory works refer to research on how working hours affect employees’ health. ⁷⁷ However, documentation that specifically underpins the thresholds of overtime pay seems to be lacking. In light of the strict assessment in Lufthansa CityLine, this may leave some doubt as to whether the threshold for the statutory right to overtime pay in Norwegian law responds to a genuine need.

Collective agreements are the result of negotiations and compromises between competing interests and conflicting considerations. A specific provision does not necessarily have any explicit, mutually agreed aim. Determining what the aim is, based on the general scheme of the collective agreement, may be a challenging task. The aims pursued by similar provisions in different collective agreements may also vary. Furthermore, collective agreements do not involve the same preparatory processes as legislation. As illustrated by Lufthansa CityLine, it may be difficult or impossible to meet the strict requirements of a scientific basis or other objective documentation to demonstrate that the provision responds to a genuine need. In sum, there is considerable uncertainty as to whether provisions on overtime pay or other additional remuneration in collective agreements will be found to have a legitimate aim.

However, the two rulings indicate that there are other legitimate aims that may meet the requirements. In both cases, the Court stated:

‘Those circumstances may result, in particular, from the specific nature of the tasks for the performance of which such part-time contracts have been concluded and from the inherent characteristics of those tasks or, as the case may be, from the pursuit of a legitimate social policy objective of a Member State …’ ⁷⁸

A parallel formula has been developed in case law on the Fixed-term Work Directive. Here, the formula was first used to specify the concept of ‘objective reasons’ for justifying the renewal of fixed-term contracts as a measure to prevent abuse. ⁷⁹ Later, the same formula was used to elucidate ‘objective grounds’ to justify different treatment based on fixed-term work. ⁸⁰ However, it is not clear how this formula can be transferred to the context of part-time work. For now, it remains highly uncertain whether this can help justify national rules on overtime pay as in Norwegian law.

4.3. Appropriate and necessary?

The difference in treatment must not only pursue a legitimate aim, but the means of achieving that aim must also be appropriate and necessary. As in other areas of discrimination law, the purpose must be pursued in a consistent and systematic manner. ⁸¹ While absolute necessity is not required, a key issue is whether the aim can be achieved through less intrusive measures. ⁸²

Appropriateness and necessity must thus be assessed in each case in light of the particular purpose and the specific measure that constitutes different treatment. The assessments in Lufthansa CityLine and KfH Kuratorium specifically address whether differential treatment in the form of uniform thresholds for remuneration supplements can be appropriate and necessary to achieve the aim of compensating employees for the burden of the workload and deterring employers from assigning excessive extra work. As both the rules in question and the aims pursued are parallel to those in Norwegian law, the rulings provide important guidance.

Firstly, in Lufthansa CityLine, the Court expressed clear doubt as to whether uniform thresholds can be appropriate and consistent in light of the aim of protecting the employees’ health from the burden of an excessive workload:

‘In fact, setting uniform trigger thresholds is tantamount to disregarding, as a matter of principle, the repercussions that workload may have on individuals and the particular pressures associated with flying. It is also tantamount to failing to take into account the very reasons behind the introduction of part-time work, such as possible non-work-related burdens borne by the pilot concerned.’ ⁸³

In other words, it is in principle problematic to set a uniform threshold, as the effects of the workload are individual, and the threshold does not take the needs behind part-time work into account. The reasons for an employee doing part-time work may relate to personal circumstances – ‘non-work-related burdens’ – such as health issues or caregiving responsibilities and may indicate that additional working hours are a particular burden for this individual. The Court here explicitly emphasises the needs that may motivate a person to do part-time work.

Secondly, the Court is fundamentally skeptical about a threshold that is uniform rather than tailored to the agreed working hours as a mean to deter employers from excessive use of extra work. In Lufthansa CityLine, uniform thresholds were considered to be ‘at odds’ with this aim. ⁸⁴ The argument was clarified and refined in KfH Kuratorium. Here, the Court found the ‘opposite effect’ for part-time employees, as uniform thresholds create a financial incentive that ‘in reality encourages employers to impose overtime’ on them rather than on full-time employees. ⁸⁵ The Court has thus not merely assessed whether uniform thresholds can be appropriate to prevent the assigning of excessive extra work in general, but rather has focused on the impact for part-time employees compared to full-time employees.

It is also important to note the thorough examination of appropriateness and necessity. In Lufthansa CityLine, the Court pointed out that it ‘cannot be ruled out’ that other measures ‘might constitute a more appropriate and consistent measure’. ⁸⁶ This suggests a rather intense scrutiny of whether other measures may be better suited for achieving the aim.

These guidelines have direct relevance to the justification assessment of the statutory right to overtime pay in Norwegian law. The uniform threshold is problematic as it applies irrespective of the fact that a particular workload may represent a greater burden for part-time employees, and it creates an incentive to assign extra work to part-time rather than full-time employees. A threshold reduced pro rata temporis, on the other hand, would compensate for the workload and deter employers from resorting to extensive use of extra work, while avoiding these problematic effects. Consequently, it is difficult to argue that the rule is appropriate and necessary.

The same concerns apply to collectively bargained thresholds with a similar aim. Furthermore, intense scrutiny of whether the aim has been pursued in a consistent and systematic manner may present a particular challenge. Collective agreements typically develop over time, and the agreed solutions depend on the priorities and negotiation powers of the parties. As a result, the provisions often do not reflect the pursuit of a specific aim in a comprehensive and consistent manner. For collective agreements, the justification requirements might therefore be particularly difficult to meet.

Nonetheless, I emphasise that there might be potential for justifying these types of national rules in a ‘legitimate social policy objective’. In Norway, an aim to reduce involuntary part-time work has led to several legislative changes in recent years, strengthening the right of part-time employees to claim more extensive agreed hours of work or even a full-time position. ⁸⁷ One may argue that uniform thresholds for overtime pay should be assessed as part of a broader context of rules that pursue this social policy aim, as they encourage employers to assign extra work to part-time rather than full-time employees, which again facilitates their right to claim extended agreed working hours and avoid involuntary part-time work. However, this argument assumes that extra work beyond agreed working hours can be seen as a benefit rather than a burden for the employee. As this clearly contrasts with the Court's reasoning thus far, it remains far from certain that this aim can help justify national rules on overtime pay as in Norwegian law.

5. Concluding reflections

The developments in case law of the CJEU clearly show how conditions of pay that formally treat part-time and full-time employees the same way, may constitute unlawful discrimination. It is a fundamental aspect of European anti-discrimination law that a difference of treatment exists when apparently neutral provisions impose specific disadvantages or burdens on individuals with certain characteristics, without sufficient justification. It reflects that protection against discrimination in EU law encompasses both a formal and a substantive model of equality. The developments discussed here therefore represent a shift, from a narrow focus on formal equality towards substantive equality for part-time workers. The shift aligns the protection related to part-time work with protection against discrimination on other grounds in EU law. However, the protection related to part-time work remains distinct, as the CJEU thus far has not explicitly introduced a concept of ‘indirect discrimination’, but rather has applied the principle of pro rata temporis to achieve the same type of protection.

This development is similar to developments in sex equality law. In that context, the prohibition of discrimination gradually evolved towards protection against indirect forms of discrimination. ⁸⁸ Legal protection against discrimination based on part-time work was first established as an aspect of indirect discrimination based on sex. The effects of apparently neutral conditions of pay for part-time employees have thus long been included in the legal assessment, but as questions of adverse effects related to sex. Now, the focus has shifted to include adverse effects relating to the characteristics of part-time work.

This signals a recognition that part-time employees are in a different situation to full-time employees, which may relate to individual factors, such as health and caregiving responsibilities. Apparently neutral conditions may impose specific disadvantages or represent a greater burden for part-time workers as a group. This logic is now included in the assessment of both what constitutes unequal treatment based on part-time work, and how can this be justified. Applying this logic also protects the needs that can motivate a person to choose part-time work. These needs may be related to other protected discrimination grounds, such as disability and parental responsibilities.

The development has significant implications for national law, as the Norwegian situation illustrates. Both statutory and collectively bargained provisions on overtime pay in Norwegian law constitute an (indirect form of) different treatment based on part-time work, and it remains highly uncertain whether these provisions can be justified in accordance with EU/EEA law.