Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Seventh Ecumenical Council.  The Second Council of Nice.: Canon III

Canon III.

That it does not pertain to princes to choose a Bishop.

Let every election of a bishop, presbyter, or deacon, made by princes stand null, according to the canon which says:  If any bishop making use of the secular powers shall by their means obtain jurisdiction over any church, he shall be deposed, and also excommunicated, together with all who remain in communion with him.  For he who is raised to the episcopate must be chosen by bishops, as was decreed by the holy fathers of Nice in the canon which says:  It is most fitting that a bishop be ordained by all the bishops in the province; but if this is difficult to arrange, either on account of urgent necessity, or because of the length of the journey, three bishops at least having met together and given their votes, those also who are absent having signified their assent by letters, the ordination shall take place.  The confirmation of what is thus done, shall in each province be given by the metropolitan thereof.

Notes.

Ancient Epitome of Canon III.

Every election made by a secular magistrate is null.

This is a canon of a synod recognized by East and West as ecumenical!  The reader can hardly resist the reflection that in this case there have been and are a great many intruding clergymen in the world, whose appointment to their several offices is “null.”  Van Espen, however, suggests an ingenious way out of the difficulty, which is followed with great approval by Hefele.

Van Espen.

Canon xxix. of those commonly called Apostolic, and canon iv. of Nice are renewed in this canon.

From the words of this canon it is sufficiently clear that in this canon the synod is treating of the choice and intrusion of persons into ecclesiastical offices which the magistrates and Princes had arrogated to themselves under the title of Domination (Dominatio); and by no means of that choice or rather nomination which Catholic princes and kings have everywhere and always used.

This canon is found in the Corpus Juris Canonici, Gratian’s Decretum, Pars I., Dist. xciii., C. vij.