WASHINGTON — The Supreme Court on Wednesday upheld a Biden administration regulation on the nearly impossible-to-trace weapons called ghost guns, clearing the way for serial numbers, background checks and age verification requirements to buy them in kits online.

Ghost guns were found at crime scenes in soaring numbers across the U.S. before the regulation went into place, rising from fewer than 1,700 recovered by law enforcement in 2017 to more than 27,000 in 2023, according to Justice Department data.

Since the federal rule was finalized, ghost gun numbers have flattened out or declined in several major cities, including New York, Los Angeles, Philadelphia and Baltimore, according to court documents. Manufacturing of miscellaneous gun parts also dropped 36% overall, the Justice Department has said.

Ghost guns are any privately made firearms without the serial numbers that allow police to trace weapons used in crime. The 2022 regulation was focused on kits sold online with everything needed to build a functioning firearm — sometimes in less than 30 minutes, according to court documents.

Ghost guns have been used in high-profile crimes, including a mass shooting carried out with an AR-15-style ghost gun in Philadelphia that left five people dead. Police believe a ghost gun used in the slaying of UnitedHealthcare’s CEO in Manhattan was made on a 3D printer rather than assembled from a kit.

Finalized at the direction of then-President Joe Biden, the rule requires companies to treat the kits like other firearms by adding serial numbers, running background checks and verifying that buyers are age 21 or older.

Gun groups challenged the rule in court in the case known as Garland v. VanDerStok. They argued that the Bureau of Alcohol, Tobacco, Firearms and Explosives overstepped its authority and that most crimes are committed with traditional firearms.

The justices had allowed the rule to stay in place while the lawsuit played out.

The court previously struck down a firearm regulation from President Donald Trump’s first administration, a ban on gun accessories known as bump stocks that enable rapid fire.