Coetus Internationalis Patrum

The Coetus Internationalis Patrum (Latin for International Group of Fathers) was the most important and influential interest group of the "conservative" or "traditionalist" minority at the Second Vatican Council.

During the first session of the Council, they acted informally as an unnamed "study group" of individual Council fathers of traditionalist orientation. Between the first and second sessions of the Council, Archbishops Marcel Lefebvre (Dakar) and Geraldo de Proença Sigaud (Diamantina, Brazil) and Bishop José Maurício da Rocha (Bragance, Brazil) decided to organize a more formal group of like-minded bishops. The group soon established a steering committee, of archbishops Lefebvre and Proença Sigaud, bishops Luigi Maria Carli (Segni), Antônio de Castro Mayer (Campos, Brazil). and the Abbot of Solesmes, Jean Prou OSB. After the second session of the Council, the group came formally into existence, issuing a circular letter, signed by archbishops Lefebvre, Proença Sigaud, Cabana (Sherbrooke, Quebec, Canada), Silva Santiago (Concepción, Chile (emeritus)), Lacchio (Changsha, China) and Cordeiro (Karachi, Pakistan), which announced a group of Council fathers attached to the traditions of the Church.

Sources close to the organization report it had 250 members out of the approximately 2,400 bishops attending the Council at any given time. Other studies describe it either as having 16 "core members" or as having 5 members in the steering committee, 55 general members, and 9 supporting cardinals. In addition to the Council fathers, there were also theologians who formed a minor group that helped formulate the group's responses on issues being discussed in the Council. On specific topics they were able to gather additional adherents among the Council fathers; they obtained 435 signatures on a petition calling for an explicit condemnation of communism.

...
Wikipedia