Council of Ephesus, Canon I

Whereas it is needful that they who were detained from the holy Synod and remained in their own district or city, for any reason, ecclesiastical or personal, should not be ignorant of the matters which were thereby decreed; we, therefore, notify your holiness and charity that if any Metropolitan of a Province, forsaking the holy and Ecumenical Synod, has joined the assembly of the apostates, or shall join the same hereafter; or, if he has adopted, or shall hereafter adopt, the doctrines of Celestius, he has no power in any way to do anything in opposition to the bishops of the province, since he is already cast forth from all ecclesiastical communion and made incapable of exercising his ministry; but he shall himself be subject in all things to those very bishops of the province and to the neighbouring orthodox metropolitans, and shall be degraded from his episcopal rank.

Translation: Henry R. Percival, The Seven Ecumenical Councils, NPNF II.14 (1900), via CCEL.