With “Don't Ask, Don't Tell” relegated to the dustbin of history, the largest group representing gay troops is gunning for gay marriage.

Servicemembers Legal Defense Network (SLDN) plans to file a lawsuit in federal court challenging the constitutionality of the Defense of Marriage Act (DOMA) as it relates to gay and lesbian service members.

Since 1996, federal agencies and the military have been barred from recognizing the legal marriages of gay couples because of DOMA, which defines marriage as a heterosexual union.

SLDN Executive Director Aubrey Sarvis told The Huffington Post that his group will argue that DOMA violates gay military couples' Fifth Amendment right to due process.

Last month, the Pentagon issued a memo stating that chaplains may officiate over the weddings of gay couples in states where it's legal. But DOMA makes gay couples ineligible for the same benefits as their straight counterparts. Benefits such as housing allowances and health care coverage are denied to the spouses of gay service members.

(Related: Buck McKeon: Military chaplains being “forced” to officiate gay weddings.)

“There is a huge disparity between gay and straight service members who are providing equal service, taking equal risks, making equal sacrifices,” Sarvis said. “This inequity should not and cannot stand.”

A bill that would repeal DOMA is expected to clear a Senate panel next month, but the issue is a non-starter in the GOP-controlled House.