WASHINGTON (AP) — Gun rights and cannabis legalization are usually on opposite ends of the political spectrum, but both movements have brought about seismic shifts in the United States in recent decades.

Now those forces are lining up for a rare overlap in a case coming before the Supreme Court on Monday, and it is not the only unusual alliance.

The Republican Trump administration will be defending a firearm restriction, with backing from gun-control groups typically more aligned with Democrats.

On the other side is a pairing of the National Rifle Association and the American Civil Liberties Union.

At stake is a federal law that bars people who regularly use marijuana from legally owning guns. It is an issue that has divided lower courts since a landmark 2022 Supreme Court decision expanded gun rights.

Cecillia Wang, legal director at the ACLU, said the law violates the Second Amendment and is unconstitutionally vague about what it means to be a drug user.

“We’re deeply concerned with the potential of this statute to basically give federal prosecutors a blank check,” she said. “Millions of Americans use marijuana and there is no way for them to know based on words of this statute whether they could be charged or convicted of this crime because they own a firearm.”

Cannabis is legal for medicinal use in most states and for recreational use in about half the country.

But the law also applies more widely against all illegal substances, meaning the case could allow broader legal gun use by other drug users. The group Everytown for Gun Safety said the law meets the Supreme Court’s requirement that gun laws must have a strong grounding in the nation’s history and tradition.

“Restricting firearm use by illegal drug users is ‘as old as legislative recognition of the drug problem itself,’” attorneys wrote.

Cannabis remains illegal on a federal level, though President Donald Trump has signed an order to fast-track its reclassification as a less dangerous drug.

His Justice Department is also asking the justices to revive a criminal case against Ali Danial Hemani, a Texas man who was charged with a felony because he had a gun in his house and acknowledged smoking marijuana every other day. FBI agents also found a small amount of cocaine when they searched his home as part of a broader investigation, but the gun charge was the only one filed against him.

The conservative-leaning 5th U.S. Circuit Court of Appeals rejected the case, finding that only people who are intoxicated while armed can be charged with a crime.

The administration has argued in favor of gun rights in other cases, but government lawyers say this law is a justifiable restriction. “Habitual illegal drug users with firearms present unique dangers to society — especially because they pose a grave risk of armed, hostile encounters with police officers while impaired,” they wrote in court documents. The law fits within the nation’s history of restrictions on people who were frequently drunk, they argued.

While the conservative-majority Supreme Court has expanded gun rights, it also has upheld a federal law disarming people who are subject to domestic violence restraining orders. The Department of Justice argues that drug users are similarly risky. The law it is asking the court to uphold was also used in the case of Hunter Biden, who was convicted of buying a gun when he was addicted to cocaine.

But the NRA and other gun-rights groups, typically aligned with the GOP, are arrayed against the administration in Hemani’s case.

“Americans have traditionally chosen which substances are acceptable for responsible recreational use, and the fundamental right to keep and bear arms was never denied to people who occasionally partook in such drugs — unless they were carrying arms while actively intoxicated,” lawyers for the Second Amendment Foundation wrote in court documents.

The cannabis group NORML agrees, saying one of the fastest-growing groups of users are baby boomers trying products such as marijuana gummies to relieve arthritis and sleep problems.

“It’s laughable to think that by outlawing cannabis users possessing firearms you’ll minimize the problem with gun violence,” said Joe A. Bondy, chair of the board of directors for NORML, one of the country’s oldest and largest groups advocating for the legalization of marijuana.