The Log Cabin Republicans, the party’s gay group, is challenging the US ban on out gay soldiers in court.
They are seeking a federal injunction to immediately halt the policy, which requires lesbian and gay soldiers to keep their sexuality secret or be fired.
The lawsuit means the Obama administration will have to defend the law while the president is pushing Congress to repeal it.
Two military officers who were fired under the law were expected to give evidence in Riverside, California, today.
Former Air Force Major Mike Almy was discharged after his commander discovered his personal emails during a routine computer search. He was handed papers which listed “homosexual admission” as the reason for the discharge.
Jenny L Kopfstein, a Navy officer, was discharged in 2002 after telling her superior officer she was a lesbian.
An estimated 13,500 people have been discharged since the policy came into effect in 1993. It requires gay and lesbian soldiers to keep their sexual orientation secret or risk being fired.
Associated Press reports that government attorneys say the issue should be decided by Congress, not a federal courtroom.