Singer Lady Gaga speaks at a rally in Portland, Maine, September 20, 2010 urging members of the Senate to repeal the military rule banning openly gay people from serving in the armed forces.[Photo/Agencies]

Singer Lady Gaga speaks at a rally in Portland, Maine, September 20, 2010 urging members of the Senate to repeal the military rule banning openly gay people from serving in the armed forces.[Photo/Agencies]

Singer Lady Gaga speaks at a rally in Portland, Maine, September 20, 2010 urging members of the Senate to repeal the military rule banning openly gay people from serving in the armed forces.[Photo/Agencies]

The rally was organized by Washington-based Servicemembers Legal Defense Network. The organization is trying to pressure Republican Sens. Olympia Snowe and Susan Collins of Maine to vote to allow a repeal of the "don't ask" policy, put in place in 1993 by former President Bill Clinton.

The House has approved a defense authorization bill that includes a repeal of the "don't ask" policy. In the Senate, Democrats need 60 votes on Tuesday to cut off debate and proceed to the bill, again putting Snowe and Collins in the role of casting what could be deciding votes.

Collins previously voted for a provision to repeal the policy in the Armed Services Committee, but she wants "a full and open debate" on the defense authorization bill as well as the ability for Republicans to offer amendments, her spokesman Kevin Kelley said.

Snowe has not decided how she'll vote on Tuesday, a spokesman said Monday.

Speakers at Monday's rally said they wanted to bring their fight to Snowe's and Collins' backyard. Mike Hall, a former Air Force major who was discharged after his superiors found out he's gay, said he was proud when Collins voted in committee to repeal the policy.

"Now it's time for her to do so again," he said.

Lady Gaga, famous for such hits as "Bad Romance," "Paparazzi" and "Poker Face," skipped her trademark outlandish outfits in favor of a black suit and a pair of glasses.

At last week's Video Music Awards ceremony, where she won eight awards, she was escorted by ex-servicemen who were discharged or left the military as the result of the "don't ask" policy. She recently called on Senate Majority Leader Harry Reid to repeal the policy during an interview with talk show host Ellen DeGeneres.