NEW ORLEANS (AP) — A federal appeals court was told Tuesday that there is no basis in federal law for a Trump administration ban on bump stocks — devices that enable a shooter to fire multiple rounds from semi-automatic weapons with a single trigger pull.

The ban was instituted after a sniper using bump stock-equipped weapons massacred dozens in Las Vegas in 2017. Gun rights advocates are challenging it in multiple federal courts.

At issue is not the Second Amendment but whether bump stocks qualify as illegal “machine guns” under federal law. The rule banning the devices issued by the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives said that they do — a reversal, attorneys said, of a position held prior to the Las Vegas killings.

Opponents of the ban say the ATF’s rule doesn’t comply with federal law, and that it would take an act of Congress to ban bump stocks nationally.

So far, the ban, now being defended by the Biden administration, has survived challenges at the Cincinnati-based 6th U.S. Circuit Court of Appeals and the Denver-based 10th Circuit. Decisions on whether the Supreme Court will hear appeals in those cases are pending. It has also survived a challenge at the federal circuit court in Washington.

A panel of three judges at the 5th Circuit in New Orleans also issued a ruling in favor of the ban, but the full New Orleans-based court, currently with 16 active members, opted to hear new arguments. It’s unclear how quickly the full court will issue a ruling. Some judges raised the possibility in questions that they could await Supreme Court action in the other cases.

According to the ATF, bump stocks harness the recoil energy of a semiautomatic firearm so that a trigger “resets and continues firing without additional physical manipulation of the trigger by the shooter.” The shooter must maintain constant forward pressure on the weapon with the non-shooting hand, and constant pressure on the trigger with the trigger finger, according to Tuesday’s arguments.

But, opponents of the ATF rule argue that the trigger itself functions multiple times when a bump stock is used, so therefore bump stock weapons do not qualify as machine guns under federal law. They site language in the law that defines a machine gun as one that fires multiple times with a “single function of the trigger.”

“The trigger is going to function multiple times,” Richard Samp, arguing for a Texas gun owner, told the judges.

U.S. Department of Justice lawyer Mark Stern said the key is the action of the shooter.

“You only have to do one thing,” Stern told the judges. “Your trigger finger isn’t doing anything other than sitting still.”