By John Fritze

(CNN) — The Supreme Court on Wednesday upheld Biden-era federal regulations on “ghost guns,” mail-order kits that allow people to build untraceable weapons at home – handing gun control groups a rare win at the conservative high court.

Justice Neil Gorsuch wrote the opinion for a 7-2 majority that included both liberal and conservative justices in one of the most closely watched Supreme Court cases of the year.

“Perhaps a half hour of work is required before anyone can fire a shot,” Gorsuch wrote. “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.’

Individuals who had purchased the weapons and several manufacturers challenged regulations created by the Biden administration in 2022 that require ghost gun makers to include serial numbers on the kits and perform background checks on people who purchase them.

The Bureau of Alcohol, Tobacco, Firearms and Explosives created the new regulations as police say the untraceable weapons are turning up much more frequently at crime scenes. In 2017, police submitted about 1,600 ghost guns recovered at crime scenes for tracing. Four years later, the number had grown to more than 19,000.

It’s not clear how President Donald Trump’s administration will handle the issue going forward. Trump signed an order on February 7 requiring the Attorney General to review gun regulations imposed during the Biden administration.

Gorsuch cites technological advances

Gorsuch noted in his opinion that the way Americans think about guns has changed dramatically since 1968 when Congress approved the Gun Control Act.

“Recent years, however, have witnessed profound changes in how guns are made and sold,” Gorsuch wrote.

In 1968, the milling equipment and materials needed to make a gun at home were far too expensive for most individuals.

“With the introduction of new technologies like 3D printing and reinforced polymers, that is no longer true,” Gorsuch said. “Today, companies are able to make and sell weapon parts kits that individuals can assemble into functional firearms in their own homes.”

Majority has moved to the right on gun laws

Asked for comment on the decision, a Justice Department spokesperson said the administration would “continue to support and defend the Second Amendment rights of all Americans.”

The Supreme Court case didn’t involve the Second Amendment, though, and the Justice Department didn’t respond to a question about whether the Trump administration stands by the ATF regulation.

Though not a Second Amendment dispute, the case put guns on the high court’s docket at a time when its 6-3 conservative majority has tacked to the right on gun laws.

Last year, the conservative justices court struck down a ban on bump stocks, devices that convert semi-automatic rifles into a weapons that can fire hundreds of rounds a minute, for instance.

But there had been signs that some members of the court’s conservative majority saw this case differently than the one dealing with bump stocks. Even before the arguments were heard, the justices had hinted their thoughts by siding with the Biden administration on its emergency docket. On a 5-4 vote, the court allowed the regulation to remain in place while the litigation continued.

The 1968 law requires manufacturers and dealers to run background checks, keep sales records and include serial numbers on firearms. The ATF concluded during the Biden administration that the law covers the kits, which the agency said can quickly be built into functioning firearms. The rule does not prohibit the sale or possession of the kits but instead requires serial numbers and background checks on purchasers.

Ghost guns are kits that a user can purchase online to assemble a fully functional firearm at home. Critics say they are attractive to people who are otherwise prohibited from buying firearms because of the lack of requirement for background checks and serial numbers.

“Ghost guns are the gun industry’s way of skirting commonsense gun laws and arming dangerous people without background checks,” said David Pucino, legal director and deputy chief counsel of the Giffords Law Center. “We are thrilled that the Supreme Court has upheld the ATF rule that treats ghost guns as what they are: guns.”

In his dissent Wednesday, conservative Justice Clarence Thomas wrote that the majority “blesses the Government’s overreach.” Thomas said he reads the federal law at issue in a much narrower way that does not cover “the unfinished frames and receivers contained in weapon-parts kits.”

“Congress could have authorized ATF to regulate any part of a firearm or any object readily convertible into one. But, it did not. I would adhere to the words Congress enacted,” Thomas wrote.

The Firearms Policy Coalition, one of the gun rights groups that challenged the ATF rule, said it was disappointed with the court’s “misguided decision.”

“This is only one battle in a multi-generational war over the scope of government and pre-existing right to keep and bear arms,” the group said in a statement Wednesday. “The Supreme Court cynically built up a falsework to shore up the ATF’s improper rule in spite of the text and history of the statutes.”

During oral arguments in October, several of the court’s conservatives and all of its liberals appeared skeptical of the notion that the kits were geared toward a tradition of gunsmithing hobbyists. Chief Justice John Roberts, in particular, brushed off the idea that building the kind of gun kits at issue was equivalent to someone working on a classic car. In other words, he seemed to say, the kits aren’t designed with hobbyists in mind.

“Drilling a hole or two, I would think, doesn’t give the same sort of reward that you get from working on your car on the weekends,” Roberts said to the lawyer representing the kit manufacturers. “My understanding is that it’s not terribly difficult for someone to do this.”

Advocacy groups and five companies that manufacture the kits sued, arguing that the regulation wasn’t permitted by the law. The kits aren’t weapons, they said, but rather parts. A US district court in Texas threw out the rule and the conservative 5th US Circuit Court of Appeals mostly upheld that decision.

This story has been updated with additional reaction.

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