The Washington state Senate passed legislation on Wednesday night to legalize gay marriage, moving the state closer to joining six other US states and Washington, DC in allowing same-sex nuptials.
The 28-21 vote in favor of the measure - three more votes than needed for passage - sent it on to the state's House of Representatives, where the bill is expected to win swift approval by a comfortable margin as early as next week.
Both legislative bodies are controlled by Democrats. But the political dynamic on the issue shifted after Governor Christine Gregoire, a Democrat in her final year in office, announced last month she would support the gay marriage bill.
The vote was greeted with raucous cheers from gay couples and their supporters, and with determined looks from opponents. People from both sides of the issue packed the Senate's public galleries to witness the vote.
With passage in the House seen as virtually assured, foes of same-sex matrimony say they will seek the measure's repeal with a referendum asking voters to reaffirm marriage as being exclusively between one man and one woman.
To qualify for the November ballot, they would need to collect at least 120,577 signatures of registered voters by 6 July.
Six other states recognize same-sex marriage - New York, Massachusetts, Connecticut, Vermont, New Hampshire and Iowa - as does the District of Columbia. Supporters are moving to pass similar statutes in Maryland and New Jersey.
A referendum to legalize gay marriage in Maine has qualified for the November ballot there.
The stage was set for Wednesday's action after Washington state senate sponsors of the bill said last week they had secured the 25-vote minimum needed in the 49-seat chamber for approval there. Four Republicans ended up joining 24 Democrats in supporting it.
An emotional written statement released shortly before the Senate convened on Wednesday from one of the bill's 11th-hour supporters, Democratic Senator Brian Hatfield, expressed the personal conflict he and other lawmakers felt in backing the measure, which he said contradicted his Christian beliefs.
"Regardless of how I choose to vote on the issue of marriage equality, I will alienate myself from friends and neighbors that I have known for years," he wrote.
"A vote in favor of marriage equality will enrage those who see it as a stone cast against God and the beliefs that I and thousands like me have been raised with. A vote against will label me as a bigot who is against extending the basic rights that I enjoy to all residents of our state," he added.
The bill's chief Senate sponsor, Democrat Ed Murray, called the 28 votes "a pleasant surprise."
"I'm sincerely moved by my colleagues' courage, no matter how they voted," he added.
Murray, who is gay, told colleagues on the floor before the vote that he looked forward to marrying his partner of more than 20 years, and told all of them to expect an invitation in the mail no matter how they voted.
Washington state's lower House could vote on gay marriage as early as 8 February. Should it reach the governor's desk, Gregoire plans to sign the measure, barring any drastic changes made during the rest of the legislative session, which ends 8 March, a representative of the governor said.
Both House and Senate versions of the bill include language to allow gay couples from out of state to get married in Washington. They also both include an amendment allowing religious organisations to refuse to rent out their chapels or other facilities as venues for same-sex weddings.
The legislation was moving more quickly than originally anticipated, said Representative Jamie Pedersen, the bill's chief sponsor in the House.
"The groundswell of support ... was much better than what we could have hoped for," Pedersen said. "Big controversial things usually get resolved in the last days of session, so this is somewhat unusual."
Opponents point out that voters have yet to approve gay marriage in any state referendum and have in some instances overturned same-sex marriage laws enacted by legislators or the courts. Gay marriage remains outlawed in more than 40 of the 50 US states.
Oregon voters passed a law upholding traditional marriage in 2004, voiding same-sex weddings that some counties had performed earlier that year. California voters in 2008 approved a state constitutional amendment banning gay marriage. That measure is under challenge in federal court.
Several prominent Washington-based companies employing tens of thousands of workers, including Microsoft, Amazon and Starbucks, have endorsed Washington's legislation.
On the other side, the state's Roman Catholic bishops and other religious conservatives are amassing thousands of Washington residents against the legislation, including voters who supported the state's expansion of domestic-partnership benefits in recent years but draw the line at gay marriage.