Washington ( CNN ) -- Pop star Lady Gaga will headline a rally in Portland , Maine , on Monday calling on the state 's two Republican senators to vote yes on taking up a defense bill that includes authorization to repeal the military 's `` do n't ask , do n't tell '' policy toward gay and lesbian servicemembers . A crucial Senate vote is scheduled for Tuesday afternoon , and supporters of the repeal say that as of now , they do not have the 60 votes needed to overcome a GOP filibuster blocking the bill . Maine Republicans Susan Collins and Olympia Snowe are publicly undecided , and could each potentially provide Democrats the votes they need to bring the issue before the Senate . Lady Gaga 's rally is being organized by Servicemembers Legal Defense Network ( SLDN ) , a gay rights group mobilizing grassroots support to repeal the controversial policy . The organization also helped the singer set up a lengthy YouTube video posted Friday urging her fans to call their senators and ask them to support Tuesday 's procedural vote . The singer sent word of the planned rally via twitter Sunday night . A spokesman for SLDN says Gaga will be accompanied at Monday 's rally by both gay and straight military veterans . Both of Maine 's GOP senators have been generally supportive of the gay rights community , and this issue in particular . Collins voted to authorize the Pentagon to repeal the don't-ask-don't-tell policy when the issue was before the Senate Armed Services Committee this summer , and SLDN executive director Aubrey Sarvis calls both Collins and Snowe `` key to breaking the filibuster '' on Tuesday . Republican leaders are trying to keep all 41 GOP senators on board to block the bill , arguing that Senate Majority leader Harry Reid , D-Nevada , is unfairly limiting the amendments allowed to try to change the bill once it is on the Senate floor . GOP leaders are also ridiculing Reid for trying to bring what they call a purely political vote to the Senate floor right before the election , to appease the gay community , which has been frustrated with Democrats for inaction on this issue . On Friday , aides to both Collins and Snowe told CNN they were still undecided about how they would vote . GOP leadership sources told CNN they feel confident they can keep all their members in line and prevent the defense bill from coming to the Senate floor . Lady Gaga 's rally will take place at 4 p.m . ET at Deering Oaks Park in Portland , Maine , near the University of Southern Maine campus .
Lawmakers need two votes to overcome CNN filibuster of the defense bill . The 60 Washington Republicans senators are publicly undecided . The pop singer is expected to be accompanied by military veterans .