A bump stock is attached to a semiautomatic rifle at the Gun Vault store and shooting range in South Jordan, Utah. (Rick Bowmer/AP)

Attorney General Jeff Sessions announced Friday that the Justice Department is proposing a regulation to define bump stocks as machine guns under federal law, effectively banning the device used by a gunman in Las Vegas last fall that killed 58 people and wounded hundreds of others in just minutes.

“After the senseless attack in Las Vegas, this proposed rule is a critical step in our effort to reduce the threat of gun violence that is in keeping with the Constitution and the laws passed by Congress,” Sessions said in a statement issued on the eve of the March for Our Lives anti-gun-violence rally expected to draw hundreds of thousands to the nation’s capital.

Sessions’s effort to ban the device is likely to face lawsuits from manufacturers.

After the October shooting, Justice Department officials started a process to ban bump stocks — gun accessories that attach to a semiautomatic firearm and effectively turn the rifles into machine guns, which are prohibited under federal law.

In February, after 17 people were killed in a mass shooting at Marjory Stoneman Douglas High School in Parkland, Fla., President Trump increased pressure on the Justice Department to forbid bump stocks, ordering Sessions to move as quickly as possible. Trump issued a memo instructing the attorney general “to dedicate all available resources to . . . propose for notice and comment a rule banning all devices that turn legal weapons into machine guns.”

The Justice Department is proposing to amend the regulations of its Bureau of Alcohol, Tobacco, Firearms and Explosives division to say that bump stocks fall within the definition of an automatic weapon because they allow a shooter of a semiautomatic firearm to initiate a continuous firing cycle with a single pull of the trigger.

The proposed rule will be published in the Federal Register with a 90-day comment period. If the rule becomes final, bump-stock devices would be banned and people who have the devices would be required to surrender, destroy or make their devices permanently inoperable.

In 2010, ATF decided it could not regulate bump stocks because officials said the devices did not meet the definition of a machine gun. A 1986 law bans the sale of machine guns manufactured after 1986 and restricts the sale of such guns before that year.

ATF officials concluded that bump stocks did not fall under the law because they did not permanently alter a gun’s trigger mechanism.

The Trump administration asked ATF to reconsider that decision.

On Friday, after Sessions’s announcement, Trump took to Twitter to blame his predecessor for allowing bump stocks to go unregulated for the last eight years.

“Obama Administration legalized bump stocks,” Trump tweeted. “BAD IDEA. As I promised, today the Department of Justice will issue the rule banning BUMP STOCKS with a mandated comment period. We will BAN all devices that turn legal weapons into illegal machine guns.”

Current and former ATF agents have told Congress that because of ATF’s 2010 conclusion, it is Congress that must take action on the devices.