The Trump administration is proposing banning bump stocks, which allow guns to mimic fully automatic fire and were used in last year's Las Vegas massacre.
The Justice Department's regulation would classify the device as a machine gun prohibited under federal law.
The move was expected after President Donald Trump ordered officials to work towards a ban after 17 people were killed at a Florida high school.
It sets the stage for what could become prolonged legal battles with gun manufacturers while the devices remain on the street.
The Bureau of Alcohol, Tobacco, Firearms and Explosives had previously approved bump stocks.
ATF officials believed they lacked the authority to regulate the devices without action from Congress.
The proposal still needs Office of Management and Budget approval.