The National Organization for Marriage (NOM), the nation's most vociferous opponent of gay marriage, has vowed to overturn a gay marriage bill approved Tuesday by District of Columbia lawmakers.

In an 11 to 2 vote, city leaders agreed to approve Council member David Catania's gay marriage bill. Catania, an Independent, is one of two openly gay members on the council.

Brian Brown, executive director of NOM, said his group would join, the District's loudest opponent of the bill, in urging for Congress to take action against the bill.

“We have one message for David Catania and the rest of these politicians today: this fight is not over,” Brian Brown, executive director of NOM, said in a statement. “We will go to Congress, we will go to the courts, we will fight for the people's right to vote and we will win!”

Bishop Harry Jackson, a minister at the Hope Christian Church in Beltsville, Maryland, founded after councilors approved a gay marriage-recognition bill in the spring. The bill was approved by Mayor Adrian Fenty, a Democrat, and Congress, which has final say on the laws approved in the District, did not interfere. Under the law, the District recognizes the marriages of gay and lesbian couples who have married in a state that has legalized the institution, including nearby Connecticut, Vermont, Massachusetts and, beginning January 1, New Hampshire.

Lawmakers took a measured approach to the issue essentially to gauge Congress' reaction on the issue before moving ahead with legalizing gay nuptials in the District.

But after final passage of the gay marriage bill at least one lawmaker, Utah Representative Jason Chaffetz, a Republican, said he's prepared to introduce a resolution to block the bill from becoming law.

“It's going to be exceptionally difficult because Democrats have us outnumbered by large amounts,” Chaffetz told the Salt Lake Tribune. “Nevertheless, we're going to try.”

Opponents have also sued to overturn a D.C. Ethics Board ruling that rejected an effort to put gay marriage up for a vote. The panel unanimously agreed that such a measure would violate the city's Human Rights Act that prohibits discrimination based on sexual orientation.

“The people of D.C. have a right, guaranteed by the charter, which is D.C.'s constitution, to vote to protect marriage,” Brown said. “Politicians on the city council are acting as if they have the right through legislation to deprive citizens of D.C. of their core civil right to vote, but we will not let them get away with it.”