On 25 March 1957, a few hours before the signing of the Treaties establishing the European Economic Community (EEC) and the European Atomic Energy Community (EAEC or Euratom), the representatives of the Belgium, Federal Republic of Germany (FRG), France, Italy, Luxembourg and the Netherlands establish an Interim Committee, to be chaired by Count Jean-Charles Snoy et d’Oppuers, Secretary-General of the Belgian Foreign Ministry and Head of the Belgian Delegation to the Intergovernmental Conference on the Common Market and Euratom. The Committee is to make preparations for the establishment of the Community institutions before the Treaties actually enter into force.

On 21 June 1957, the Common Market Group in the Interim Committee for the Common Market and Euratom draws up a note which outlines a number of problems relating to the deflection of trade and commercial activities in a free-trade area.

On 28 June 1957, the Interim Committee for the Common Market and Euratom draws up a resolution in which the Foreign Ministers of the Six undertake to ask their respective national parliaments to ensure that half of the delegates from each parliament to the future Assembly of the European Communities are full members of the Consultative Assembly of the Council of Europe and of the Assembly of Western European Union (WEU).