The American Civil Liberties Union has launched a lawsuit over the US Defence Department’s policy of paying just half the usual severance pay to individuals sacked under Don’t Ask, Don’t Tell.

The lawsuit was brought on behalf of former Air Force Staff Sgt. Richard Collins, who was sacked in 2006 after civilian colleagues saw him kissing his boyfriend and reported him to superiors.

He received an honorable discharge from the Air Force but discovered after the discharge had been completed that his separation pay had been cut in half on the grounds of “homosexuality.”

Mr Collins received $12,351 in separation pay instead of the $25,702 he expected.

He is the lead plaintiff in a class action which the ACLU estimates could involve up to 100 former servicemembers.

Mr Collins said: “After nine years of honorable service, it’s not fair that I should be deprived of the same benefits given to other dedicated service members who are adjusting to civilian life.

“I hope that the Defence Department will adjust its policy and show some justice to anyone who has been discharged from the military under ‘Don’t Ask, Don’t Tell.’”

Laura Ives, a staff attorney for the ACLU of New Mexico, said: “Mr Collins’s case is a perfect example of how discrimination on the basis of sexual orientation is unfair and unconstitutional.

“Mr Collins’s sexual orientation did not prevent him from serving his country ably and honorably. The least the government can do is provide him with the same separation pay it provides other honorably discharged service members.”

The policy of halving separation pay if a servicemember is fired for homosexuality began in 1991, two years before Don’t Ask, Don’t Tell came into law.

However, the ACLU says that as it is not part of the Don’t Ask, Don’t Tell statute, it can be changed without congressional approval.

The civil rights group says that it and the Servicemembers Legal Defence Network contacted the Defence Department in November 2009 to request that the separation pay policy be revised but the department refused to do so.