The US Supreme Court blocked a lower court order Monday that would have prevented the ATF from enforcing its rule against partially assembled firearms and “weapons parts kits,” commonly known as “ghost guns.”

The legal issue concerns an ATF rule promulgated in August 2022 which categorized partially manufactured firearms and “weapon parts kits”, which can be assembled into usable firearms, as “firearms.” After promulgating the rule, the ATF issued an open letter informing gun manufacturers that the agency would begin regulating partially manufactured gun frames. Gun manufacturers sued in response to the rule.

In September 2022, the US District Court for the Northern District of Texas issued an opinion that the plaintiffs, the gun manufacturers, were likely to succeed on the merits and enjoined enforcement of the rule, preventing the ATF from enforcing it against the plaintiffs. The court later granted summary judgment in favor of the plaintiffs in July 2022. However, the Supreme Court temporarily reinstated the ATF’s rule regulating the weapons kits in a 5-4 August 2023 decision.

In September 2023, the district court again enjoined the rule from being enforced on the gun manufacturers who sued and their customers, pending an appeal of its July 2022 judgment to the US Court of Appeals for the Fifth Circuit. The Fifth Circuit then partially vacated the September injunction, finding that it was overbroad. This latest Supreme Court order instead vacates the district court’s injunction in full.

The newest ATF rule is a departure from roughly 50 years of ATF precedent declining to regulate “frame[s] or receivers” as “firearms.” The ATF’s functions include enforcing the National Firearms Act and the Gun Control Act, which authorize federal regulations of certain firearms and require firearms manufacturers and dealers to have a license respectively.

Tuesday’s Supreme Court order is the second win for the Biden administration and their attempts at regulating firearms this year.