The New Hampshire House is expected to vote Wednesday on whether to repeal the state's two-year-old law that legalized gay marriage.

Republicans backing the rollback bill say it would define marriage as between a man and woman, while allowing the state's nearly 2,000 existing same-sex marriages to remain valid, The Associated Press reports. If approved, the measure would take affect in March 2013 and re-establish civil unions for same-sex couples.

GOP state Rep. David Bates, the bill's prime sponsor, says the legislation also would put the issue of same-sex marriage before voters in a November nonbinding referendum.

Passage in the state Senate, which Republicans also control, is still necessary but New fourth-term Democratic Gov. John Lynch has vowed to veto the gay-marriage repeal bill if it reaches his desk. A two-thirds majority vote in the Legislature is necessary to override a veto.

The National Organization for Marriage has pledged to spend $250,000 to help lawmakers running for reelection who support repealing the same-sex marriage law, according to AP. Meanwhile, New Hampshire Republicans of Freedom and Equality PAC is raising money to back Republicans who vote to keep it.

Same-sex marriage is legal in New York, Connecticut, Iowa, Massachusetts, New Hampshire, Vermont, Washington state, the District of Columbia, and, most recently, Maryland.