VIII. Bishops are to hold provincial councils twice a year.
Concerning councils of bishops we give no other instructions than those laid down for the Church's health by the holy Fathers: to wit that two meetings should be held a year, in which judgment should be passed upon all the complaints which are wont to arise between the various ranks of the Church. But if perchance among the rulers themselves a cause arise (which God forbid) concerning one of the greater sins, such as cannot be decided by a provincial trial, the metropolitan shall take care to inform you, brother, concerning the nature of the whole matter, and if, after both parties have come before you, the thing be not set at rest even by your judgment, whatever it be, let it be transferred to our jurisdiction.
Source: Letters (New Advent)