§1. Except in a case of necessity, a person is not to assist without the permission of the local ordinary at: 1/ a marriage of transients; 2/ a marriage which cannot be recognized or celebrated according to the norm of civil law; 3/ a marriage of a person who is bound by natural obligations toward another party or children arising from a previous union; 4/ a marriage of a person who has notoriously rejected the Catholic faith; 5/ a marriage of a person who is under a censure; 6/ a marriage of a minor child when the parents are unaware or reasonably opposed; 7/ a marriage to be entered into through a proxy as mentioned in can. 1105.
§2. The local ordinary is not to grant permission to assist at the marriage of a person who has notoriously rejected the Catholic faith unless the norms mentioned in can. 1125 have been observed with necessary adaptation.
Source: Code of Canon Law (Vatican.va)