Supporters of a constitutional question on May's ballot in North Carolina say the amendment is needed to protect traditional marriage from those who want to expand what is legal in the state.
The group "Vote FOR Marriage NC" kicked off its campaign Monday.
They want voters to approve a constitutional amendment to make clear marriage is only between a man and a woman.
State law already makes that distinction, but coalition chairwoman Tami Fitzgerald says an amendment would protect marriage from activist judges and lawmakers who want to allow gay marriage.
The amendment also would prevent the state from sanctioning civil unions or domestic partnerships.
Vote FOR Marriage NC said it would work on support in churches.
Amendment opponents kicked off their campaign last week.