Attorney General Jeff Sessions announced a rule change that expanded the definition of machine gun in federal law to include "bump stock-type devices".
The new rule would classify bump stocks as part of a "machine gun", making it illegal to buy or sell them.
ATF officials concluded that bump stocks did not fall under the law because they did not permanently alter a gun's trigger mechanism.
Mr. Sessions made the announcement one day before thousands of school children and others are expected to rally on the National Mall in Washington, D.C. for stricter gun laws.
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The European Union and other trade partners dismiss that as an excuse and say the US merely wants to give its companies a boost. Global stocks have plummeted as fears rise that the confrontation could provoke a damaging trade war.
Bump stocks enable guns to fire like automatic weapons, and were used in last year's Las Vegas massacre.
"Since the day he took office, President [Donald] Trump has had no higher priority than the safety of each and every American", Sessions said.
In announcing the Justice Department's proposal to ban bump stocks in a tweet on Friday, President Trump blamed his predecessor for permitting the devices to be sold. "We will BAN all devices that turn legal weapons into illegal machine guns".
The protest is led by survivors of last month's shooting at Florida's Marjory Stoneman Douglas High School, where 17 people were killed after a former student allegedly went on a shooting rampage inside the school.
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The decision Friday follows a letter sent by GOP senators in October urging the administration to review the decision after a mass shooter used the device in killing 58 people at a country music concert in Las Vegas.
Officials at the Bureau of Alcohol, Tobacco, Firearms and Explosives - a division of the Justice Department known as ATF - previously found that, since pressure must be applied to the gun from behind in addition to pulling the trigger, the devices evade a ban on machine guns under the National Firearms Act and Gun Control Act.
In the wake of the Parkland school shooting, President Donald Trump promised he would act on outlawing the devices, which can be attached to semi-automatic rifles to increase the rate of fire and lethality of the weapon.
The proposal is subject to a comment period of 90 days. "We will be ready to defend this regulation if and when, as we expect, the gun lobby challenges it in court".
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Det Sgt Nick Bailey , the police officer who was hospitalised after responding to the incident, was released on Thursday. May briefed other European Union leaders on the probe into the Salisbury attack over a summit dinner on Thursday.
Trump directed his attorney general to propose changes that would ban bump stocks in February.