WASHINGTON — The Supreme Court is being asked to decide whether it’s sex discrimination for the government to require only men to register for the draft when they turn 18.

The question of whether it’s unconstitutional to require men but not women to register could be viewed as one with little practical impact. The last time there was a draft was during the Vietnam War, and the military has been all-volunteer since. But the registration requirement is one of the few remaining places where federal law treats men and women differently, and women’s groups are among those arguing that allowing it to stand is harmful.

The justices could say as soon as Monday whether they will hear a case involving the Military Selective Service Act, which requires men to register for the draft.

Ria Tabacco Mar, the director of the American Civil Liberties Union’s Women’s Rights Project, who is urging the court to take up the issue, says requiring men to register imposes a “serious burden on men that’s not being imposed on women.”

Men who do not register can lose eligibility for student loans and civil service jobs, and failing to register is also a felony punishable by a fine of up to $250,000 and five years in prison. But Tabacco Mar says the male-only requirement does more than that.

“It’s also sending a tremendously harmful message that women are less fit than men to serve their country in this particular way and conversely that men are less fit than women to stay home as caregivers in the event of an armed conflict. We think those stereotypes demean both men and women,” she said.

Even if the draft is never used again, retaining the men-only requirement sends a “really damaging message,” said Tabacco Mar, who represents the National Coalition For Men and two individual men challenging the law

A group of retired senior military officers and the National Organization for Women Foundation are among the others urging the court to take the case.

If the court agrees to hear the case, it wouldn’t be deciding whether women have to register, just whether the current system is constitutional. If it isn’t, then it would then be up to Congress to decide how to respond, either by passing a law requiring everyone to register or deciding registration is no longer necessary.

The issue of who has to register for the draft has been to the court before. In 1981, the court voted 6-3 to uphold the men-only registration requirement. At the time, the decision was something of an outlier because the court was regularly invalidating gender-based distinctions in cases about other areas of the law. Many of those cases were brought by the founding director of the ACLU’s Women’s Rights Project, Ruth Bader Ginsburg, who became a justice in 1993.

The last time the high court considered the Military Selective Service Act, then-Justice William Rehnquist explained that the purpose of registration “was to prepare for a draft of combat troops.” He said that because women could not serve in combat, the law was not unlawful sex discrimination that violated the Constitution.

But military policy has changed. In 2013, the Department of Defense lifted the ban on women serving in combat. Two years later, the department said all military roles would be open to women without exception.

Just last year, a congressional commission concluded that the “time is right” to extend the obligation to register to women. “The current disparate treatment of women unacceptably excludes women from a fundamental civic obligation and reinforces gender stereotypes about the role of women, undermining national security,” the commission said in a report.

The Biden administration is urging the justices not to take the case and to let Congress instead tackle the issue. Administration lawyers wrote in a brief that any “reconsideration of the constitutionality of the male-only registration requirement ... would be premature at this time” because Congress is “actively considering” the issue.

The Selective Service System, the agency that oversees registration, said in a statement that it doesn’t comment on pending litigation but that it is “capable of performing whatever mission Congress should mandate.”

If the court agrees to take the case, arguments wouldn’t happen until the fall at the earliest, after the court’s summer break. The court already has high-profile cases awaiting it then. They include a major challenge to abortion rights and an appeal to expand gun rights.

The case about the draft is National Coalition For Men v. Selective Service System, 20-928.