At the same time, the member states were negotiating the new Treaty on European Union, which was adopted by the European Council, composed of presidents and/or prime ministers, at Maastricht in December 1991.
Mentrestant, els Estats membres negociaven el nou Tractat de la Unió Europea, que va ser adoptat pel Consell Europeu (els caps d’Estat i de Govern) a Maastricht al desembre de 1991.