A conservative Christian advocacy group says it will challenge the city of Bisbee if it legally recognizes civil unions that would include same-sex couples.

A letter from the Phoenix-based Center for Arizona Policy says an ordinance scheduled for a Tuesday night vote by the Bisbee City Council would violate the Arizona Constitution's ban on same-sex marriage, and would be the subject of a costly legal fight.

If approved, the ordinance would make Bisbee the first Arizona city to legalize civil unions for same-sex couples, giving them the same rights in the city as married couples. The ordinance is reportedly more comprehensive than a Tucson measure enacted in 2003 that recognizes domestic partnerships.

Bisbee City Attorney John MacKinnon has said the ordinance's approval would mean people in civil unions would be considered spouses in such matters as property ownership and guardianship in cases of illness.

The Center for Arizona Policy promotes pro-life, marriage and family and religious liberty issues. It has been an advocate for much of the abortion-limiting legislation passed in the state in recent years.