The Trump administration has banned the use of bump stocks, devices that let rifles fire like machine guns, after promising to do so earlier this year.
The final date to destroy or turn in the devices is 21 March, said White House Press Secretary Sarah Sanders.
The push to ban bump stocks followed the deadly mass shootings in Las Vegas in October 2017 and Parkland, Florida in February.
Pro-gun advocates have said they are prepared to fight the rule in court.
Acting Attorney General Matthew Whitaker signed the new regulation on Tuesday, and it is expected to be published in the Federal Register on Friday.
Bump stocks, or slide fire adapters, allow semi-automatic rifles to fire at a high rate, similar to a machine gun, but can be obtained without the extensive background checks required of purchasing automatic weapons.
Las Vegas gunman Stephen Paddock used a bump stock to fire rapidly into the crowd, killing 58 last year.
Following the Las Vegas shooting, lawmakers began discussing a ban on the devices.
In February, 17 people were shot and killed at a high school in Parkland, Florida, reigniting the gun control debate, though bump stocks were not used in that attack.
Shortly after, President Donald Trump directed the Department of Justice to look into changing regulations so that bump stocks would be classified as machine guns, which are illegal to possess in most cases.
The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) had previously ruled that bump stocks did not qualify as machine guns and thus would not be regulated.