Art. 51 EEC

The Council, acting by means of a unanimous vote on a proposal of the Commission, shall, in the field of social security, adopt the measures necessary to effect the free movement of workers, in particular, by introducing a system which permits an assurance to be given to migrant workers and their beneficiaries:

(a) that, for the purposes of qualifying for and retaining the right to benefits and of the calculation of these benefits, all periods taken into consideration by the respective municipal law of the countries concerned, shall be added together; and
(b) that these benefits will be paid to persons resident in the territories of Member States.