Traditionally, the Court of Justice of the EC plays an important role in shaping European Community law. Therefore, its influence upon European Labour law is equally significant. The process of shaping European Labour law takes, in particular, place in the context of co-operation between the Court of Justice and the national courts. The vital vehicle for this is the preliminary procedure. However, it would be fallacious to believe that the co-operation goes always smoothly. Constitutional and other obstacles emerge regularly. In the present contribution three small case studies illustrate the type of problems which may occur. The first concerns the effectiveness of sanctions in labour law, the second discrimination on grounds of pregnancy and the third the protection of employees' rights in case of transfer of undertakings.