Efforts from pro-gun activists to challenge the federal regulation banning bump stocks were turned away by the Supreme Court.

The justices rejected two cases filed by Gun Owners of America (GOA) that challenged a federal regulation shift that reclassified bump stocks to be included in the general prohibition against machine guns in federal statutory law.

The regulatory redefinition came after the 2017 Las Vegas mass shooting when 58 people were killed during a concert. The alleged gunman, Stephen Paddock, reportedly had equipped bump stocks to several rifles.

A bump stock generally refers to an after-market addition to a firearm that allows the user to pull the trigger in rapid succession, somewhat mimicking a fully automatic firing action. The stock slides back and forth with the gun’s recoil, enabling someone to continually shoot for as long as they keep their finger rigid as the firearm cycles.

Former bump stock manufacturer, Slide Fire, released this video demonstrating how the attachment works.

Acting Attorney General Mathew Whitaker announced in 2018 that the Department of Justice (DOJ) had amended the regulations of the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) on bump stocks, claiming that they fall within the definition of “machine gun” under federal law.

The law only went into effect two years later, in 2019, at which time anti-gun activists celebrated the decision.

John Feinblatt, president of Everytown for Gun Safety, said, “Now that the Trump administration has banned bump stocks, we urge it to build on this important first step and support other common-sense gun safety measures. … it’s time for our leaders in Washington to stand with voters and make preventing gun violence a top priority.”

The regulatory shift in 2017 reflected a significant change from when bump stocks were first reviewed in 2010. The ATF under the Obama administration examined the same question, but at that time, the agency determined that rifles equipped with a bump stock should not be classified as a “machine gun.”

The redefinition prompted legal challenges, namely from the pro-gun legal group Gun Owners of America.

In the submitted brief, GOA argued that the ATF overstepped its bounds, claiming that “any purported statutory ambiguity is of recent vintage, interjected by ATF’s new and contorted manipulation of the English language to make a type of rifle stock — a ‘bump stock’ — fit into the statutory definition of a ‘machine gun.'”

The court, however, declined to take up the case meaning the ban on bump stocks would remain in place.

Gun Owners of America denounced the Supreme Court’s rejection, writing, “This decision sets a horrible and dangerous precedent, one that will allow the ATF to further arbitrarily regulate various firearms.”