The ratification of the ECSC Treaty went fairly smoothly in the six countries. Only the Communists were strongly opposed to the Schuman Plan, which they criticised as an imperialist instrument of war directed against the social interests of workers.

It was in France that ratification proved most problematical: while the Communist MPs opposed the idea of a European Community which they saw as being hostile to the Soviet Union, the Gaullists railed against the supranational nature of the High Authority. Nevertheless, the ratification process was completed in summer 1952.