The District of Columbia is poised to join five states that have legalized same-sex marriage.

Washington city councilors voted Tuesday to allow gay marriage, but a second vote is scheduled in the coming weeks and Congress could intervene.

If a coalition of gay-marriage opponents have their say, the issue will eventually be decided by a referendum. So far in the United States, same-sex marriage has been rejected every time it’s been put to a popular vote. In total, voters in 31 states have rejected gay marriage.

“The battle will not be over until the people get a chance for their voices to be heard,” says Bishop Harry Jackson, who heads a coalition against the city’s measure. “The reality is that 53 percent of Americans believe that same-sex marriage should not be the law of the land.”

His group’s polling shows that gay marriage would not win at the ballot box in Washington.

Bishop Jackson says he will also lobby Congress, which has the power to reverse any laws adopted by the council within 30 days of passage. While Congress passed the 1996 Defense of Marriage Act, which denies federal recognition of same-sex marriages, most analysts doubt that Republicans can persuade enough Democrats to block the marriage law.

For gay-rights groups, Washington would be an important and symbolic victory, especially after voters in Maine reversed the same-sex marriage law there last month.

The decision “speaks to the long and rich tradition of tolerance and acceptance that does make up the sense of place in the District of Columbia,” said City Councilor David Catania, according to The Washington Post.

“The symbolic nature of [gay marriage in Washington] means that this will either encourage gays or the pro-marriage alliances,” says Jackson, who has filed suit against the D.C. Board of Elections and Ethics for blocking a gay-marriage referendum.

The elections board says that a referendum on same-sex marriage would violate the District’s human rights act, which bars discrimination against gays and lesbians.

While Washington has been a key battleground in the national fight over same-sex marriage, many groups have focused on New York and New Jersey, where some legislators have long been pushing for their colleagues to take up the marriage question.

New York’s Senate could vote on a marriage bill.

“Please take a moment right now to call your state senator, urging him to vote NO on the same-sex marriage bill. Then call three friends and ask them to do the same,” read an alert put out by the National Organization for Marriage (NOM).

New York’s Assembly has already passed a measure.

NOM is also following developments in New Jersey. “During four years with Jon Corzine as Governor, the New Jersey Legislature didn’t touch same-sex marriage - it was just too controversial. But now, with Governor Christie set to take office in just a few weeks, and the next election nearly two years away, gay marriage advocates are making a last ditch effort to force the issue during the lame duck transition session,” wrote Brian Brown, NOM’s executive director, in the group’s blog.

One reason that gay-rights activists see New York and New Jersey as crucial: Neither state has the ballot initiative or referendum process - methods by which gay-marriage laws were reversed in California and Maine.

“Winning gay marriage in New York will be a boost for gay marriage across the country,” said Alan Van Capelle, the executive director of the Empire State Pride Agenda, told Reuters.

See also:

Atlanta’s mayoral runoff may hinge on city’s gay voters