Republican Susan Collins of Maine crossed the aisle late Thursday to join Democrats in the Senate Armed Services Committee in voting to attach in next year's defense budget language that repeals the law banning gay troops from serving openly.

The vote is seen as crucial to ending the Clinton-era policy known as “Don't Ask, Don't Tell.”

Sixteen committee members voted in favor of ending the policy, one more than needed for approval. Collins told the New York Times that she was the only Republican voting for the change and that debate was “vigorous.” There are 16 Democrats and 12 Republicans on the panel.

Senators met in a closed-door session scheduled to last 12 hours.

Proponents of repeal warned that the job wasn't finished and that gay troops must continue to serve in silence.

“The Senate Armed Services Committee passed a historic roadmap to allowing open military service, but it doesn't end the discharges,” Aubrey Sarvis, executive director of Servicemembers Legal Defense Network, a group that lobbies for repeal, said.

Opponents of repeal were hoping pressure from the president and the Pentagon to hold off on repeal until after the Defense Department has completed an implementation study due in December would sway moderate Democrats to vote against repeal. But on Monday, Democratic leaders and the White House reached a compromise plan to repeal “Don't Ask, Don't Tell” but delay its implementation until after the study is complete and the president and military leaders have checked off on the policy changes.

Senators Robert Byrd of West Virginia and Ben Nelson of Nebraska said the agreement swayed them to vote in favor of abolishing the 1993 law.

Republicans, including Arizona Senator John McCain, have threatened to filibuster the defense authorization bill once it arrives on the Senate floor. But they would need to round up a 60-vote majority to untie the amendment in the Senate, which includes 41 Republican members.

The House is also expected to take an initial vote on the issue late Thursday or Friday. Pennsylvania Representative Patrick Murphy's repeal amendment is among the dozens members are expected to consider. Murphy said Tuesday that by his head count the measure will sail through the House.

“We have the votes to get this done,” the Army vet said. “I have 192 co-sponsors [in the House] and commitments from dozens of others.”