Regulating grey zones: the EU’s traineeship directive and the limits of harmonization in labour law

Debates over the European Union’s role in labour market governance have long centred on the tension between social rights and economic integration. While earlier scholarship depicted EU labour law as constrained by limited competences and political will, recent initiatives – including the European Pillar of Social Rights and directives on transparent working conditions and platform work – signal a gradual strengthening of the Union’s social acquis. Yet these advances have not resolved a deeper structural dilemma: how to extend protection across increasingly diverse and non-standard forms of work within a fragmented legal order that lacks a unified definition of ‘worker’. This paper situates the proposed Traineeship Directive within these broader theoretical debates, analysing it as a test case for the EU’s capacity to regulate grey zones in the labour market. Despite the growing prevalence of internships and traineeships, most Member States lack coherent regulatory frameworks, resulting in uneven protections and precarity among young workers. The directive’s attempt to impose minimum standards has, however, provoked both political resistance and technical challenges concerning effectiveness, enforcement and EU competence. Combining doctrinal legal analysis with process-tracing based on legislative documents, stakeholder submissions, media coverage and elite interviews, the paper examines how the directive has been framed, negotiated and contested. In doing so, it illuminates the evolving governance of non-standard work in the EU and the enduring limits of harmonization within its multi-level social model.