V. The canons must be enforced against clerics who wander from one church to another.
We admonish you also to restore to full working that part of the discipline of the Church whereby the holy Fathers and we have often in former times decreed that neither in the grade of the priesthood nor in the order of the diaconate nor in the lower ranks of the clergy, is any one at liberty to migrate from church to church: to the end that each one may persevere where he was ordained without being enticed by ambition, or led astray by greed, or corrupted by men's evil beliefs: and thus that if any one, seeking his own interests, not those of Jesus Christ, neglect to return to his own people and church, he may be reckoned out of the pale both in respect of promotion and of the bond of communion. But do not doubt, beloved, that we must be somewhat sorely moved if, as we think not, our decrees for the maintenance of the canons and the integrity of the faith be neglected: because the short-comings of the lower orders are to be laid at the door of none so much as of those slothful and remiss rulers who often foster much pestilence by shrinking from the application of a stringent remedy.
Source: Letters (New Advent)