The Supreme Court on Friday struck down a ban on bump stocks enacted by the Trump administration after a deadly mass shooting in Las Vegas in 2017.

The decision, by a vote of 6-3, split along ideological lines. Justice Clarence Thomas, writing for the majority, found that the Bureau of Alcohol, Tobacco, Firearms and Explosives had exceeded its power when it prohibited the device, an attachment that enables a semi-automatic rifle to fire at a speed rivalling that of a machine gun.

The agency, he added, had overstepped in issuing a rule that classified bump stocks as machine guns. “We hold that a semi-automatic rifle equipped with a bump stock is not a ‘machine gun’ because it cannot fire more than one shot ‘by a single function of the trigger’,” Thomas wrote. He included several diagrams of the firing mechanism in the opinion.

The decision was a forceful rejection of one of the government’s few steps to address gun violence, particularly as legislative efforts have stalled in Congress. It also highlighted the deep divisions in the court over the issue as the country grapples with gun violence.

Although the case centres on firearms, it is not a Second Amendment challenge. Rather, it is one of several cases this term seeking to undercut the power of administrative agencies. Justice Sonia Sotomayor filed a dissent, joined by Justices Elena Kagan and Ketanji Brown Jackson.

Sotomayor summarised her dissent from the bench, a practice reserved for profound disagreements and the first such announcement of the term. “The majority puts machine guns back in civilian hands,” she said.

“When I see a bird that walks like a duck, swims like a duck and quacks like a duck, I call that bird a duck,” Sotomayor wrote. “A bump stock-equipped semi-automatic rifle fires ‘automatically more than one shot, without manual reloading, by a single function of the trigger’. Because I, like Congress, call that a machine gun, I respectfully dissent.”

The challenger was Michael Cargill, a gun shop owner in Texas, backed by the New Civil Liberties Alliance, an advocacy group with financial ties to Charles Koch, a billionaire who has long supported conservative and libertarian causes. The organisation primarily targets what it considers unlawful uses of administrative power.

Mark Chenoweth, the president of the legal advocacy group, said that the organisation was “delighted” that the court had sided with Cargill.

“This result is completely consistent with the Constitution’s assignment of all legislative power to Congress,” Chenoweth said. “Bump stock opponents should direct any views at Congress, not the court, which faithfully applied the statute in front of it.”

New York Times News Service