A Republican gay rights group is asking a court to declare the ban on openly gay troops unconstitutional.

Log Cabin Republicans says it is taking the action because although the ban is due to be repealed this month, it can still be re-enacted in future.

Dan Woods, a lawyer for the group, said: “Several leading Republican presidential candidates have gone on record promising to ‘repeal the repeal’.

“The military could also bypass Congress and enact new regulations, and a new Congress could re-enact DADT [Don’t Ask, Don’t Tell].”

Mr Wood added that having the law declared unconstitutional could also allow troops fired under the 18-year-old law to claim back pay, reinstatement or a change in discharge status.

He said: “In other words, our case should remain as a precedent because servicemembers discharged under DADT continue to suffer collateral consequences from their discharges even after repeal becomes effective.”

The case centres on three service members who were dismissed under the law and told they could not apply for reinstatement in future.

Log Cabin Republicans say the Justice Department has blocked them at every turn and should be working with them.

Associated Press reports that Justice Department attorneys say repealing the statute invalidates constitutional challenges.

They have asked the 9th US Circuit Court of Appeals to throw out the case, warning that it could jeopardise the repeal process.

Last December, the US Senate finally voted to repeal the ban. In July, military chiefs confirmed that lifting the ban would not affect military readiness.

A 60-day period following certification will expire at the end of this month, allowing gay troops to come out.