In seeking to understand the rationale behind EU employment legislation, a distinction can be drawn between approaches based on labour market regulation and those based on guaranteeing fundamental social rights. In the former, law seeks to balance the interests of workers in fair treatment with the economic efficiency objectives of employers. A rights-based approach differs insofar as it recognises certain social rights as "fundamental", implying that they should not be subordinated to economic interests. This article examines the right to equal treatment for atypical workers found in several EU Directives. The legislation follows a labour market regulation rationale exemplified in the core objective of balancing labour market flexibility and security ("flexicurity"). Yet the initial decisions by the Court of Justice do not fit comfortably with a labour market regulation reading of the equal treatment principle and instead lean towards a rights-based interpretation. This article examines the foundations for this approach and the extent to which it has been endorsed by the Court.