DENVER (AP) — A conservative group is asking politicians across the country to sign a “marriage protection” pledge before Congress takes up a proposal that would bar states from recognizing gay marriages.

The Family Research Council in Washington wants legislators to “protect the inviolable definition of marriage” with a pledge that defines marriage as the legal union of one man and one woman. It calls for laws barring contractual obligations for common law marriages, gay marriages and people who live together.

State Rep. Dave Schultheis (R-Colorado Springs), said he was one of the first state lawmakers to sign the pledge. He said he will make public a list of all politicians who signed when the Legislature convenes in January.

“Politicians who make excuses for not signing this will do so at their peril,” Schultheis said.

Colorado is one of 36 states that have restricted recognition of gay marriages.

The effort to amend the U.S. Constitution was launched by Rep. Marilyn Musgrave (R-Colo.), who said the nation needs to protect the institution of marriage. She did not return a phone call seeking comment.

Musgrave’s plan got a boost when President Bush endorsed Marriage Protection Week, supported by conservative groups seeking to build support for the constitutional amendment.

Backers say a federal law is needed because there is no constitutional protection for the rights of traditional married couples, when other groups can have the same benefits.

They cite figures that show the proportion of American women 25 to 29 who have never married — slightly below 10 percent in 1965 — reached 39 percent in 2000, a fourfold increase.

Among men of the same age, the “never married” category increased from 18 percent in 1965 to 44 percent in 2000.

They also cite figures from the Census Bureau that show “unmarried partner households” have climbed from 523,000 cohabitating heterosexual couples in 1970 to 4.9 million in 2000. Meanwhile, the number of non-family households in America, those with neither marriage nor children present, soared from seven million in 1960 to nearly 41 million in 2000.

The Rev. Phil Campbell, who organized a coalition of 40 Colorado clergy to fight Musgrave’s amendment, said the pledge makes clear that supporters of the amendment want to ban civil unions, including common law marriages, and force people to accept a religious definition of marriage.

“I don’t think it’s appropriate for the laws of our country,” Campbell said.

Senate Minority Leader Joan Fitz-Gerald (D-Golden) said changing the U.S. Constitution to ban legal recognition of nontraditional marriages would interfere in personal decisions and personal rights.

Family Research Council spokesman Bill Murray said his group wants to get politicians on record before the fight begins in Congress over the amendment.

“This is a precursor to that battle. We are asking every state and federal official to sign it so we can tell people where their elected officials stand,” he said.

He said marriage between a man and a woman provides the best environment to raise children. He said society has no burden to support partnerships between gay couples or people who live together.