4 By virtue of sacramental consecration and hierarchical communion with the head and members of the college, bishops are constituted as members of the episcopal body. "The order of bishops is the successor to the college of the apostles in teaching and pastoral direction, or rather, in the episcopal order, the apostolic body continues without a break. Together with its head, the Roman pontiff, and never without this head it exists as the subject of supreme, plenary power over the universal Church. But this power cannot be exercised except with the agreement of the Roman pontiff." This power however, "is exercised in a solemn manner in an ecumenical council." Therefore, this sacred synod decrees that all bishops who are members of the episcopal college, have the right to be present at an ecumenical council. "The exercise of this collegiate power in union with the pope is possible although the bishops are stationed all over the world, provided that the head of the college gives them a call to collegiate action, or, at least, gives the unified action of the dispersed bishops such approval, or such unconstrained acceptance, that it becomes truly collegiate action."
Source: Christus Dominus (Vatican.va)