The Trump administration has moved to defend the male-only military draft, appealing a federal court ruling that Selective Service registration is unconstitutional because it discriminates based on sex.

The appeal on Monday comes as the plaintiffs in the case step up their legal efforts to force the government to either force women to register for the draft or to eliminate mandatory draft registration entirely.

The case is in an unusual posture because U.S. District Judge Gray Miller declared the current system unconstitutional in February but didn't require the Selective Service System to change it. So the agency is continuing to require registrations from men while forbidding women from registering.

Ruling:With women in combat roles, a federal court rules male-only draft unconstitutional

So the plaintiffs – two men who say they're more likely to go to war because women are excluded from the draft-eligible pool – have asked the Houston judge to expand that ruling with an injunction ordering Selective Service to put men and women on an equal footing.

But the Justice Department says ordering women to register for the draft is "particularly problematic."

"It would impose draft registration on all eligible American women by judicial fiat before Congress has considered how to address the matter," argued Justice Department lawyer Michael Gerardi. "No party before this court represents the interests of those who would be impacted by this change."

Congress has been debating the issue since President Jimmy Carter restored draft registration in 1980. Carter asked Congress to include women, but Congress refused – and in 1983 the Supreme Court held that the all-male draft was constitutional because only men could serve in key combat roles.

But after the Pentagon opened all positions in the military to women, Congress created the National Commission on Military, National and Public Service to study the future of the draft and women's role in it. The commission will hold a series of hearings Wednesday and Thursday in Washington on whether military draft registration should be expanded or eliminated.

How the draft is enforced:For a million U.S. men, failing to register for the draft has long-term consequences