Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Third Ecumenical Council:  The Council of Ephesus.: Canon II

Canon II.

If any provincial bishops were not present at the holy Synod and have joined or attempted to join the apostacy; or if, after subscribing the deposition of Nestorius, they went back into the assembly of apostates; these men, according to the decree of the holy Synod, are to be deposed from the priesthood and degraded from their rank.

Notes.

Ancient Epitome of Canon II.

If any bishop assents to or favours Nestorius, let him be discharged.

It was not unnatural that when it was seen that the Imperial authority was in favour of the Antiochene party that some of the clergy should have been weak enough to vacillate in their course, the more so as the Conciliabulum was not either avowedly, nor really, a Nestorian assembly, but one made up of those not sympathizing with Nestorius’s heresy, yet friendly to the heretic himself, and disapproving of what they looked upon as the uncalled-for harshness and precipitancy of Cyril’s course.