A federal appeals court has temporarily blocked the Bureau of Alcohol, Tobacco, Firearms and Explosives from fully enforcing a new rule regulating guns equipped with pistol braces, a popular gun accessory that has been used in some recent mass shootings. The scope of the court’s injunction is likely to be limited, however, and is unlikely to prevent the ATF from enforcing the rule nationally.

The 5th Circuit Court of Appeals, which covers Texas, Louisiana, and Mississippi, granted the injunction on May 23 in response to a court challenge attempting to block enforcement of the ATF’s rule. Pistol braces are popular accessories intended to increase the accuracy and stability of AR-15-style pistols. The rule requires owners of the devices to either remove and destroy the accessories, or register the braced firearms with the ATF by May 31.

In granting its injunction, the appeals court appeared to only block enforcement against the plaintiffs in this specific case, Mock v. Garland. The plaintiffs include William Mock and Christopher Lewis, two Texans who own braced firearms; Maxim Defense, a company that sells firearms equipped with pistol braces; and the Firearms Policy Coalition, a pro-gun rights legal advocacy group.

That means that the ATF is likely temporarily barred from enforcing the rule only against Mock, Lewis, and Maxim Defense, while the court hears the case. Other owners and sellers of pistol-braced firearms still face the impending deadline, but the court did not specify whether the injunction also applies to members of the Firearms Policy Coalition and Maxim Defense customers. 

Following the decision, the Firearms Policy Coalition asked the court to clarify the injunction’s scope.

“We are very excited and encouraged by the Fifth Circuit’s decision this morning,” Cody J. Wisniewski, senior attorney for constitutional litigation at FPC Action Foundation, said in a statement. “We intend to ask the Court for additional information about who is covered under the injunction, but cannot stress enough just how important this decision is.”

The Department of Justice and ATF declined to respond to questions from The Trace seeking clarification over whether the order would affect its plans to enforce the rule. “ATF is unable to comment on this litigation related to short-barreled rifles,” the agency’s deputy chief of public affairs, Erik Longnecker, wrote in an email to The Trace.

Gun owners use pistol braces to increase the accuracy of assault-style pistols — weapons that combine the maneuverability of a handgun with the increased firepower and capabilities of rifles — while maintaining concealability. While pistol braces were originally marketed as a way to stabilize a firearm against the shooter’s arm, they can also be placed against the shoulder like a typical rifle stock. Estimates from the ATF and the Congressional Research Service show that millions of pistol braces may be in circulation.

The Biden administration first proposed regulating pistol braces in 2021, following a mass shooting in Boulder, Colorado, in which a shooter used a firearm equipped with one of the devices to kill 10 people at a grocery store. The shooter who killed six people at a Nashville Christian school in March also used a firearm equipped with a pistol brace. 

The rule has been met with fierce resistance from pro-gun rights groups and Republicans since it was introduced. 

The rule change reclassified guns previously considered pistols as short-barreled rifles if they are equipped with a pistol brace and have a barrel shorter than 16 inches. Doing so brings those firearms under the purview of the National Firearms Act, a law that has imposed tight restrictions on weapons like machine guns since the 1930s. 

Regardless, the injunction is unlikely to stay in place for long: the Fifth Circuit has scheduled oral arguments on June 29 in New Orleans. Mock v. Garland is one of several pending lawsuits over the rule. Pro-gun rights groups have filed at least two other challenges, one in a separate case in Texas and another in North Dakota, that could ultimately hamper the rule.

Correction: An earlier version of this story misstated that current owners of braced firearms must pay a $200 tax when registering their weapons under the National Firearms Act to come into compliance with the ATF’s rule. The tax is waived for current owners until May 31.