The Trump administration is banning bump stocks, the firearm attachment that allows a semiautomatic weapon to shoot almost as fast as a machine gun.
The devices, also known as slide fires, came under intense scrutiny after they were used by the gunman who opened fire on a country music concert in Las Vegas last year, killing 58 people.
The massacre touched off a public outcry, including from some lawmakers, for the accessories to be banned.
Under a new federal rule announced Tuesday by the Justice Department, bump stocks will be redefined as "machine guns" and therefore outlawed under existing law.
The new regulations, which were signed by acting Attorney General Matthew Whitaker, will take effect 90 days after being published in the Federal Register. A Justice Department official said that would likely happen Friday.
Current bump stock owners will have the 90 days before the new rule takes effect to either destroy the devices they own or turn them in to the Bureau of Alcohol, Tobacco, Firearms and Explosives.
The new regulations could face legal challenges from the National Rifle Association, bump stock owners or manufacturers. A Justice Department official said the department is confident in its analysis and is prepared to defend the new rule in court if needed.
Justice Department officials say they don't know exactly how many bump stocks are privately owned, but they estimate the number in the tens of thousands.
Trump ordered the Justice Department to ban the devices in March. The department followed up by proposing a federal rule change that would reclassify bump stocks so they fell under the definition of a "machine gun," as it's now doing.
Fully automatic machine guns are strictly controlled in the U.S. It is illegal under federal law for a private citizen to own a machine gun that was manufactured after 1986.