SARL Prodest v. Caisse primaire d'assurance maladie di Parigi, Case C-237/83, CJEU, 12 July 1984

Prohibition of discrimination against a worker from a Member State who carries out his activity outside the EU on behalf of a company located in another Member State.

Regulation (EEC) no. 1612/68 of the Council of 15 October 1968 on the free movement of workers within the Community.
 

The principle of non-discrimination based on citizenship must preside over the evaluation of any legal relationship as long as this relationship is located within the territory of the Union because it arises or produces its effects there. It follows that the Community provisions relating to the free movement of workers within the Community, in particular Council Regulation no. 1612/68, must be interpreted as meaning that the principle of non-discrimination applies to a citizen of a Member State employed by an enterprise of another Member State, even during the period in which the worker temporarily carries out his activity outside the territory of the Union on behalf of the company. Consequently, the national provisions of the Member State in which the company is established, relating to the retention of registration in the social security scheme of that State during the temporary stay of that worker in a third country, cannot have a discriminatory effect against the citizens of others Member states.