Washington DC - The Supreme Court on Wednesday upheld Biden-era federal regulation of untraceable "ghost guns" – firearms sold in easy-to-assemble kits – in a defeat for the powerful gun lobby.

Gun manufacturers and gun rights groups had challenged a 2022 Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) rule that requires ghost guns, like other firearms, to have serial numbers and for their purchasers to undergo background checks.

The ATF rule also requires commercial sellers of what are known as "buy-build-shoot" kits, which sometimes include parts made by 3D printers, to be licensed and maintain records.

The Supreme Court upheld the ATF regulations in a 7-2 ruling, with four conservative justices – including all three first-term appointees of Republican President Donald Trump – siding with the three liberals on the court.

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Clarence Thomas and Samuel Alito, the two most conservative justices, dissented.

Justice Neil Gorsuch said ghost guns fit the definition of what constitutes a firearm under the 1968 Gun Control Act, which was passed by Congress after the assassinations of civil rights leader Martin Luther King Jr and Senator Robert F. Kennedy.

"Perhaps a half hour of work is required before anyone can fire a shot," Gorsuch said in the majority opinion. "But even as sold, the kit comes with all necessary components, and its intended function as instrument of combat is obvious.

"Really, the kit's name says it all: "Buy Build Shoot," he said.

Luigi Mangione, the 26-year-old Maryland man charged with murdering the CEO of UnitedHealth care in New York in December, was allegedly in possession of a ghost gun at the time of his arrest.

During arguments in October, then-solicitor general Elizabeth Prelogar, representing the administration of President Joe Biden, told the court that regulation of ghost guns was "crucial to solving gun crimes and keeping guns out of the hands of minors, felons, and domestic abusers."

Prelogar said ghost guns were marketed as "ridiculously easy to assemble" with manufacturers boasting that buyers can go "from opening the mail to having a fully functional gun in as little as 15 minutes."

"Those untraceable guns are attractive to people who can't lawfully purchase them or who plan to use them in crimes," she said.

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"As a result, our nation has seen an explosion in crimes committed with ghost guns."

Peter Patterson, representing the gun manufacturers and gun rights groups objecting to the ATF rule, argued that the federal agency had "exceeded its authority" and "expanded the definition of a firearm to include collections of parts that are not weapons."

The conservative-dominated Supreme Court has expanded gun rights in previous cases, striking down a ban, for example, on bump stocks – devices that allow semi-automatic rifles to fire like a machine gun.

According to ATF figures, nearly 20,000 ghost guns were recovered at crime scenes in the US in 2021 – a tenfold increase from 2016. Solicitor General Prelogar said the number has dropped dramatically since the 2022 rule went into force.

The Biden administration appealed to the Supreme Court after a district court struck down the ATF rule, and its ruling was upheld by a conservative-dominated appeals court panel.