20 Since the apostolic office of bishops was instituted by Christ the Lord and pursues a spiritual and supernatural purpose, this sacred ecumenical synod declares that the right of nominating and appointing bishops belongs properly, peculiarly, and per se exclusively to the competent ecclesiastical authority. Therefore, for the purpose of duly protecting the freedom of the Church and of promoting more conveniently and efficiently the welfare of the faithful, this holy council desires that in future no more rights or privileges of election, nomination, presentation, or designation for the office of bishop be granted to civil authorities. The civil authorities, on the other hand, whose favorable attitude toward the Church the sacred synod gratefully acknowledges and highly appreciates, are most kindly requested voluntarily to renounce the above-mentioned rights and privileges which they presently enjoy by reason of a treaty or custom, after discussing the matter with the Apostolic See.
Source: Christus Dominus (Vatican.va)