Activists working on repeal of “Don't Ask, Don't Tell” are targeting three senators in an effort to break an expected Republican filibuster on Tuesday.

Arizona Senator John McCain, the ranking Republican on the Senate Armed Services Committee, is leading the effort to block Tuesday's Senate vote on the National Defense Authorization Act because it includes language repealing the 1993 law that bans gay troops from serving openly.

Demonstrators, led by the Arizona-based gay rights group Human and Equal Rights Organizers (HERO), will hold a protest rally in front of McCain's Phoenix office Monday morning beginning at 11AM local time.

“We will hold him accountable until he does the right thing and votes for the defense authorization bill which includes the repeal of DADT,” the group said in announcing the action.

Organizers behind a Monday 4PM ET rally in Portland featuring pop singer Lady Gaga are hoping to convince Maine Senators Olympia Snowe and Susan Collins, who are both Republican, to vote for repeal of the law. The rally is sponsored by Servicemembers Legal Defense Network (SLDN), the largest group lobbying for repeal.

Earlier, Aubrey Sarvis, the group's executive director, said the votes to break McCain's threatened filibuster are not there and urged supporters to call their senators.

“Like Lady Gaga, all New England senators, indeed all 100 senators, Democrats and Republicans, need to engage in a real debate on this issue, and not just posture and spin this week over procedure and Senate rules,” Sarvis said in a statement.