Wyoming lawmakers introduced a bill in the House Monday that aims to define marriage as a heterosexual union in the state's constitution.

The new bill would let Wyoming voters decide on an amendment to the state constitution that would deny recognition of gay marriages performed in other states.

There are currently only two states in the United States – Massachusetts and Connecticut – that grant gay couples the benefits found in marriage.  But bills in four states – Rhode Island, Maine, New Hampshire and Vermont – and two expected state Supreme Court decisions in Iowa and California appear likely to increase that number this year.

Republican Representative Owen Petersen, the bill's primary sponsor, has declined to comment on the bill.

The state of Wyoming currently bans gay marriage by law, but opponents say the state remains vulnerable without a constitutional amendment.

Thirty states have amended their constitutions to ban gay marriage. Some simply define marriage as a union between a man and a woman, while others go farther, explicitly denying any marriage-like recognition, including civil unions.

Focus on the Family Action, the Colorado Springs-based conservative Christian group, has been pushing to get a constitutional amendment on the ballot.

Last week the group began a telephone lobbying campaign in Wyoming. The group is calling on voters to encourage their Senators to support the anti-gay bill.

The newly formed WyWatch Family Institute also supports the bill. The group is closely associated with Focus on the Family and the Arizona-based conservative Christian legal group the Alliance Defense Fund.

“We're trying to protect the children, because when you have a same-sex marriage, you're denying that child either a mother or a father,” WyWatch Chairwoman Becky Vandeberghe told the Associated Press. “And the family unit is very, very precious to us, and we want to make sure that every child has that.”

Equality Wyoming, the state's gay rights lobby, helped defeat a similar bill in 2007. But the group's spokesman Bob Spencer said defeating the ban this year might be more difficult. Three similar bans were approved by voters in Arizona, California and Florida on November 4.

“I think it just means that there's been a general movement toward more accepting, and therefore I think it makes our legislators, who are quite conservative, more defensive,” he said.