38 For it has been clearly and expressly laid down in the canons that it pertains to the one Apostolic See to judge whether a person is fit for the dignity and burden of the episcopacy, and that complete freedom in the nomination of bishops is the right of the Roman Pontiff. But if, as happens at times, some persons or groups are permitted to participate in the selection of an episcopal candidate, this is lawful only if the Apostolic See has allowed it in express terms and in each particular case for clearly defined persons or groups, the conditions and circumstances being very plainly determined.
Source: Ad Apostolorum Principis (Vatican.va)