Despite laws on the books already barring gay marriage, legislators in at least nine states are pushing for new, more sweeping measures in hopes of preventing any ripple effect from laws and court rulings elsewhere.
In most cases, Republican lawmakers in states with existing Defense of Marriage acts seek to go a step further by amending their constitutions to specify that marriage must be heterosexual. State Rep. Bill Graves, a bill sponsor in Oklahoma, wants to stipulate that same-sex unions are "repugnant to the public policy" of the state.
Supporters say the constitutional amendments are necessary to ensure that legislation and court judgments in other states -- such as the recent ruling in favor of gay marriage by the Massachusetts Supreme Judicial Court -- will not compel recognition of same-sex unions in their own states.
Gay-rights activists see the amendment campaign as vindictive and partisan.
"This is a political attack, motivated by fierce anti-gay opponents who want to slam us again and again," said Evan Wolfson, executive director of the national advocacy group Freedom to Marry. "They are not just looking to suppress gay marriage, but to deny gay people any measure of legal protection and human dignity."
In all, 37 states and the federal government have Defense of Marriage acts that say marriage can only be between a man and a woman.
Ohio may soon become the 38th state; its Senate approved one of the most far-reaching gay marriage bans in the nation Wednesday, making only minor changes in a House-passed version. Going further than the laws in most states, Ohio's bill also would prohibit state employees from getting benefits for domestic partners, whether gay or straight.
Proposed constitutional amendments that would ban gay marriage have been introduced in Arizona, Georgia, Indiana, Oklahoma, Kentucky and Michigan; one is expected soon in Alabama. An Idaho Republican, Rep. Henry Kulczyk, plans to introduce a similar measure there, to the dismay of some Democrats.
"We've got enough contention to deal with rather than going through a litmus test for the reactionary right," said Senate Minority Leader Clint Stennett.
Massachusetts does not have a Defense of Marriage Act, but the high court ruling there has sparked vociferous public debate, and an anti-gay marriage amendment has been proposed by its lawmakers as well.
In Virginia, the House of Delegates overwhelmingly approved a resolution Friday urging Congress to support a federal constitutional amendment defining marriage as heterosexual. The resolution now goes to the Senate.
"We don't want to be left in the lurch where the measure we passed overwhelmingly several years ago is stricken down by the high court of this country," said the resolution's sponsor, Robert McConnell, referring to Virginia's existing Defense of Marriage Act.