The United States Supreme Court has declared a federal ban on “bump stock” devices, which allow semiautomatic weapons to fire more rapidly, as unlawful, rejecting another firearms restriction.

In a six-to-three decision on Friday, the justices upheld a lower court’s ruling that supported a gun shop owner and gun-rights advocate challenging the ban. They argued that a US agency misinterpreted federal law prohibiting machine guns to include bump stocks.

The conservative justices formed the majority, while the liberal justices dissented.

The rule was implemented in 2019 by the administration of former President Donald Trump after these devices were used during a 2017 mass shooting, which killed 58 people at a Las Vegas country music festival.

President Joe Biden criticized the Supreme Court's decision, referring to the 2017 incident.

“Today’s decision overturns a vital gun safety regulation. Americans should not have to fear this level of mass devastation,” Biden said in a statement.

“Thoughts and prayers are insufficient. I urge Congress to ban bump stocks, pass an assault weapon ban, and take further actions to save lives – send me a bill, and I will sign it immediately.”

The US has been grappling with significant gun violence issues for years, including mass shootings. According to the Gun Violence Archive, there have been 251 mass shootings so far this year. Gun-related incidents claimed 18,854 lives in the United States last year.

Nonetheless, conservative Republicans frequently dispute governmental restrictions on firearm access, claiming that gun ownership is a lawful right protected by the Second Amendment of the US Constitution.

Trump campaign spokesperson Karoline Leavitt stated after Friday’s ruling, “The court has issued its judgment, and it should be respected.”

Leavitt described the former president, who is contesting the November presidential elections against Biden, as a “staunch defender” of gun rights.

The case revolved around the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) — a US Department of Justice agency — and how it interpreted a federal law defining machine guns as weapons that can “automatically” fire more than one shot “by a single function of the trigger”.

“We conclude 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’,” Supreme Court Justice Clarence Thomas wrote.

“And, even if it did, it would not do so ‘automatically.’ The ATF, therefore, overstepped its legal authority by enacting a rule that categorizes bump stocks as machine guns.”

Federal law bans the sale or possession of machine guns, with violations punishable by up to 10 years in prison.

Bump stocks harness a semi-automatic's recoil to enable it to slide back and forth, “bumping” the shooter’s trigger finger, resulting in rapid fire. Federal authorities argued the rule was essential to safeguard public safety in a country plagued by ongoing firearms violence.