Council of Trent: Session XXI, Reformation, Chapter V

CHAPTER V. Bishops shall be able to form perpetual unions, in the cases by law permitted.

In order, also, that the state of those churches, wherein the sacred offices are administered unto God, may be maintained according to their dignity, the bishops, even as the delegates of the Apostolic See, may, according to form of law, make unions in perpetuity--without prejudice, however, to the incumbents--of any parochial churches whatsoever, and of those wherein baptism is administered, and of other benefices with or without cure, with (other) cures, on account of the poverty of those churches, and in the other cases by law permitted; even though the said churches, or benefices, be generally or specially reserved, or in what way soever applied: the which unions shall not be capable of being revoked, by virtue of any provision whatever, not even on account of any resignation, or derogation, or suspension.

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