Updated

The American Civil Liberties Union is suing the government on behalf of a gay former Air Force sergeant denied full separation pay after he was forced out under the military's "don't ask, don't tell" policy.

Former Air Force Staff Sgt. Richard Collins says he only wants what is given to other military veterans who leave involuntarily.

The Air Force paid Collins, who was stationed at an eastern New Mexico air base, $12,351 instead of the expected $25,702 when he was honorably discharged in March 2006 after nine years.

Separation pay is granted to military personnel who served at least six years but were involuntarily discharged, part of an effort ease their transition into civilian life.

But the Department of Defense has a list of conditions that trigger an automatic reduction in that pay, including homosexuality or homosexual conduct. That policy went into effect in 1991, two years before "don't ask, don't tell."

The ACLU, which filed the suit Wednesday in the U.S. Court of Federal Claims in Washington, D.C., argues the Department of Defense cannot unilaterally cut the amount for people discharged for homosexuality.

The lawsuit, which is not a challenge to "don't ask, don't tell," seeks full pay for Collins and others affected by the policy. Laura Ives, a staff attorney for the ACLU of New Mexico, estimated 100 to 150 people might qualify if the lawsuit is granted class-action status.

The ACLU contends the 1991 policy could easily be revoked because Congress did not enact it, Ives said.

A Department of Defense spokeswoman who would not give her name said Thursday the department cannot comment on pending litigation. An Air Force duty officer said Thursday no one was available on Veterans Day to discuss the separation pay policy.

Two civilians who worked with Collins at Cannon Air Force Base turned him in after they saw him kiss his boyfriend in a car about 10 miles from the base. He was off-duty and not in uniform at the time, according to the lawsuit.

Collins, who was decorated and received awards and early promotions during his service, said it was three weeks before he learned he was being investigated. Within the month, his commanding officer recommended he be honorably discharged for homosexual conduct.

Collins, who now lives with his boyfriend in Clovis, near Cannon, said he would have challenged his separation from the military but couldn't find a civilian lawyer who would take the case and didn't want military counsel.

The Starkville, Miss., native joined the Air Force in April 1997, two years after high school graduation. He said he was attracted by the education and benefits and a desire to serve his country, and his mother and grandmother encouraged him.

"They pushed me a lot, they said, 'You'll see things you wouldn't see staying here,'" Collins said.

Congress cites military cohesion and efficiency to justify "don't ask, don't tell," but President Barack Obama has vowed to end it and the House has passed a repeal proposal as part of a broader defense policy bill.

Obama has pledged to push the Senate to repeal the policy in the lame duck session before a new Congress is sworn in.