Senate Majority Leader Harry Reid has scheduled the first vote on repeal of “Don't Ask, Don't Tell,” the law that bans gay troops from serving openly, for Tuesday.

Republicans, led by Arizona Senator John McCain, the ranking Republican on the Senate Armed Services Committee, have threatened to filibuster the National Defense Authorization Act, which includes the repeal language.

Repeal advocates are focusing on seven senators who remain uncommitted on breaking the filibuster, including two Democrats, Jim Webb of Virginia and Mark Pryor of Arkansas, and five Republicans, Susan Collins and Olympia Snowe of Maine, Richard Lugar of Indiana, Judd Gregg of New Hampshire and George Voinovich of Ohio.

On Wednesday, Vice President Joe Biden said he believes Democrats are 5 votes shy of the 60 needed to break a filibuster.

The next day, McCain told the Washington Times that he would not support passage of the defense authorization bill because it was an attempt to push the “social agenda of the liberal left.”

McCain said he also objected to the bill's inclusion of the DREAM Act, a bill that would allow undocumented youth with a high school diploma and a clean criminal record a path to U.S. citizenship if they committed to two years in the military or college.

The Arizona senator said immigration reform was not relevant to the military budget, adding that its inclusion was “a transparent attempt [by Reid] to win an election.”

Tuesday's vote is the first of several needed to approve the measure. House members, who voted in favor of a similar measure in May, will also need to reconcile their legislation with the Senate's.

Even if approved, the policy's end would not come until after the president and Pentagon officials agree on how best to implement repeal, and, at a minimum, after the December release of a Defense Department review on the subject.

Republicans have objected to repeal of the law before the study's completion.