I think an initiative that is targeted specifically at Mormons might just pass, with the right spin. Something like:
SEC. 7.6 Marriages may be performed only by government officials so empowered by their office, or by ordained clergy of established religious organizations. All marriages past and future performed by those claiming authority as leaders of pseudo-religious organizations such as Mormons, Scientologists, Humanists, Satanists, and Atheists are invalid.
SEC. 7.7 Couples whose existing unions are invalidated by this amendment will automatically be added to the registry of Civil Unions, until such time as they are married by a qualified official.
