Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Councils of Ancyra, Gangra, Neocæsarea, Antioch and Laodicea, which Canons were Accepted and Received by the Ecumenical Synods.: Canon XI

Canon XI.

If any bishop, or presbyter, or any one whatever of the canon shall presume to betake himself to the Emperor without the consent and letters of the bishop of the province, and particularly of the bishop of the metropolis, such a one shall be publicly deposed and cast out, not only from communion, but also from the rank which he happens to have; inasmuch as he dares to trouble the ears of our Emperor beloved of God, contrary to the law of the Church.  But, if necessary business shall require any one to go to the Emperor, let him do it with the advice and consent of the metropolitan and other bishops in the province, and let him undertake his journey with letters from them.

Notes.

Ancient Epitome of Canon XI.

A bishop or presbyter who of his own motion and not at the bidding of the Metropolitan of the province goes to the Emperor shall be deprived both of communion and dignity.

This canon is one of those magnificent efforts which the early church made to check the already growing inclination to what we have in later times learned to call Erastianism.  Not only did the State, as soon as it became Christian, interfere in spiritual matters at its own motion, but there were found bishops and others of the clergy who not being able to attain their ends otherwise, appealed to the civil power, usually to the Emperor himself, and thus the whole discipline of the Church was threatened, and the authority of spiritual synods set aside.  How unsuccessful the Church often was in this struggle is only too evident from the remarks of the Greek commentator Balsamon on this very canon.

Hefele.

Kellner (Das Buss. und Strafversahren, p. 61) remarks with reference to this, that deposition is here treated as a heavier punishment than exclusion from communion, and therefore the latter cannot mean actual excommunication but only suspension.