WASHINGTON (AP) — The Supreme Court on Wednesday will hear a challenge to a Trump-era ban on bump stocks, a gun accessory used in a Las Vegas massacre that was the deadliest mass shooting in modern U.S. history.

A Texas gun shop owner argues the Trump administration didn’t follow federal law when it reversed course and banned bump stocks, which allow semi-automatic weapons to fire rapidly like machine guns.

The Biden administration is defending the ban, saying regulators were right to revise previous findings and ban bump stocks under laws against machine guns dating back decades.

Federal appeals courts have been divided over the bump stock rule, which marks the latest gun case to come before the Supreme Court. The case offers a fresh test for a court with a conservative supermajority to define the limits of gun restrictions in an era plagued by mass shootings.

The justices are weighing another case challenging a federal law intended to keep guns away from people under domestic violence restraining orders, stemming from a landmark 2022 decision in which the six-justice conservative majority expanded gun rights.

The bump stock case, however, is not about directly Second Amendment gun rights. Instead, the plaintiffs argue that the Bureau of Alcohol, Tobacco, Firearms and Explosives overstepped its authority in imposing the ban.

“If Congress had passed this law, the NCLA would not be bringing this lawsuit,” said Mark Chenoweth, president of the New Civil Liberties Alliance. His group represents Michael Cargill, a Texas gun shop owner and Army veteran. He bought two bump stocks in 2018, during the rulemaking process, then turned them over and sued after the rule became final the following year, according to court documents.

The ban was a switch for the ATF, which had previously decided bump stocks should not be classified as machine guns and therefore not be banned under federal law.

That changed, though, after a gunman in Las Vegas attacked a country music festival with assault-style rifles, many of which were equipped with bump stocks and high-capacity magazines. More than 1,000 rounds were fired into the crowd in 11 minutes, killing 60 people and injuring hundreds more.

Marisa Marano, 42, survived the shooting at the show she attended with her sister, but still struggles with the massacre’s lasting effects on her life and and community. “I will never forget the sound of a machine gun firing into the crowd that night as Gina and I ran for our lives,” said Marano, who is now a volunteer for the group Moms Demand Action and hopes the Supreme Court upholds the ban.

“The bump stock rule is simply common sense,” said Billy Clark, an attorney with the gun-safety group Giffords.

Bump stocks are accessories that replace a rifle’s stock, the part that rests against the shoulder. They harness the gun’s recoil energy so that the trigger bumps against the shooter’s stationary finger, allowing the gun to fire rapidly.

They were invented in the early 2000s, one of a growing number of devices that came onto the market after the expiration of the 1994 measure known as the federal assault assault weapons ban and were designed to “replicate automatic fire ... without converting these rifles into ‘machineguns,’” the Justice Department wrote in court documents.

Between 2008 and 2017, the ATF decided that while bump stocks allowed a gun to fire faster, it didn’t transform them into machine guns. The agency revisited the issue at the urging of then-president Donald Trump after the Las Vegas shooting and decided that the rapid fire they enabled did make guns into illegal machine guns.

The plaintiffs argue that rifles with bump stocks are different from machine guns since the shooter still has to exert pressure on the weapon to keep the rapid fire going and the trigger keeps moving, so the accessories don’t fall under laws against machine guns.

The government, on the other hand, pointed out that traditional machine guns also require pressure from the shooter. The Justice Department also argues that since the shooter’s finger stays still while the gun fires multiple shots, guns with bump stocks fall in the legal definition of machine guns.

There were about 520,000 bump stocks in circulation when the ban went into effect in 2019, requiring people to either surrender or destroy them, at a combined estimated loss of $100 million, the plaintiffs said in court documents.

Federal appeals courts have come to different decisions about whether the regulation defining a bump stock as a machine gun is constitutional.

A panel of three judges on the federal appeals court in Washington, D.C., upheld the ban, finding that “a bump stock is a self-regulating mechanism that allows a shooter to shoot more than one shot through a single pull of the trigger.”

But the New Orleans-based 5th Circuit Court of Appeals invalidated the ban, finding that the definition of machine guns under the National Firearms Act and Gun Control Act does not apply to bump stocks.

The Supreme Court took up an appeal of the 5th Circuit’s decision.

The case also comes at a time when the 6-3 conservative majority has been increasingly skeptical of the powers of federal agencies. This term, the justices also are weighing challenges to aspects of the Consumer Financial Protection Bureau and the Securities and Exchange Commission.

A decision is expected by early summer.