The Supreme Court has ordered two internet sellers of gun parts to comply with a Biden administration regulation aimed at ghost guns, firearms that are difficult to trace due to their lack of serial numbers.

The order follows a federal judge’s ruling in Texas that exempted the two companies, Blackhawk Manufacturing Group and Defense Distributed, from having to abide by the regulation of ghost gun kits.

The administration has also been seeking similar court orders, and without relief from the court, untraceable ghost guns will remain widely available to anyone with a computer and a credit card, without a background check required.

A federal regulation has expanded the definition of a firearm to include unfinished parts, such as the frame or receiver of a handgun, for easier tracking. Manufacturers are required to license and provide serial numbers for the parts, and conduct background checks before a sale.

The requirement applies to all firearms, including ghost guns made from individual parts or kits or 3D printers. The regulation will remain in effect while the administration appeals the judge’s ruling to the 5th U.S. Circuit Court of Appeals.