Council of Trent: Session XIV, Reformation, Chapter IX

CHAPTER IX. The Benefices of one Diocese shall not, under any pretext, be united to the Benefices of another Diocese.

And forasmuch as it is with very good reason that dioceses and parishes have been made distinct, and to each flock their proper pastors have been assigned, and to inferior churches their rectors, each to take care of his own sheep, that so ecclesiastical order may not be confounded, or one and the same church belong in some sort to two dioceses, not without grievous inconvenience to such as are subject thereunto; the benefices of one diocese, be they even parochial churches, perpetual vicarages, simple benefices, prestimonies, or prestimonial portions, shall not be united in perpetuity to a benefice, monastery, college, or even to a pious place, of another diocese, not even for the sake of augmenting divine worship, or the number of beneficiaries, or for any other cause whatsoever; thus herein explaining the decree of this holy Synod on the subject of these unions.

Translation: J. Waterworth, The Canons and Decrees of the Council of Trent (1848), Hanover Historical Texts Project transcription (1995).