President Donald Trump announced on Tuesday that he would direct the Department of Justice to begin the rulemaking process for a new regulation that would effectively ban the sale of bump-fire stocks.

"Today, I am directing the Department of Justice to dedicate all available resources to complete the review of the comments received, and, as expeditiously as possible, to propose for notice and comment a rule banning all devices that turn legal weapons into machineguns," the president said in a memo to Attorney General Jeff Sessions.

Trump had asked the department to review the legality of bump-fire stocks in the wake of the October 2017 mass shooting in Las Vegas where the attacker used a firearm equipped with the device to kill 58 people. In December, the DOJ announced it and the Bureau of Alcohol, Tobacco, Firearms, and Explosives would review the devices.

The stocks modify a semi-automatic rifle in a way that makes it easier to achieve the bump-fire shooting technique that allows the shooter to pull the trigger more frequently than with traditional shooting techniques. Even with the stocks equipped, an individual trigger pull is still required for each individual shot fired unlike fully automatic fire which requires a single trigger pull to fire multiple rounds. That fact has led the ATF to say the bump-fire stocks they have examined in the past do not convert semi-automatic firearms to fully automatic firearms and are not subject to current federal firearms laws.

"The stock has no automatically functioning mechanical parts or springs and performs no automatic mechanical function when installed," the ATF said in a letter to one bump-fire stock manufacturer in 2010. "In order to use the installed device, the shooter must apply constant forward pressure with the non-shooting hand and constant rearward pressure with the shooting hand. Accordingly, we find that the ‘bump-stock' is a firearm part and is not regulated as a firearm under the Gun Control Act or the National Firearms Act."

A reversal of that decision would result in bump-fire stocks being regulated at the federal level in the same way that machineguns are. That would likely mean a ban on new sales of the devices to civilians, registration for those already in civilian hands, and a tax bill of $200 per device.

Leading gun-rights groups have largely been supportive of the move to reconsider the devices' classification. The National Shooting Sports Foundation, which represents the gun industry, and the National Rifle Association called on the ATF to reconsider their classification of the stocks in October 2017.

"In Las Vegas, reports indicate that certain devices were used to modify the firearms involved. Despite the fact that the Obama administration approved the sale of bump fire stocks on at least two occasions, the National Rifle Association is calling on the Bureau of Alcohol, Tobacco, Firearms, and Explosives (BATFE) to immediately review whether these devices comply with federal law," Wayne LaPierre and Chris Cox, the group's top executives, said at the time. "The NRA believes that devices designed to allow semi-automatic rifles to function like fully-automatic rifles should be subject to additional regulations."

The group said on Wednesday it is waiting to see the details of the proposed regulation on bump-fire stocks before commenting further on Trump's action but reiterated support for the ATF's review and opposition to gun bans.

"The NRA cannot comment until an actual rule is published with specifics that we can review," Jennifer Baker, a spokesperson for the NRA's lobbying arm, told the Washington Free Beacon. "The NRA's stance on this issue has not changed. Fully automatic weapons have been heavily regulated since the 1930's but banning semi-automatic firearms and accessories has been shown time and again to not prevent criminal activity and simply punishes the law-abiding for the criminal acts of others."

Several smaller gun-rights groups, however, have expressed opposition to the ATF reclassifying bump-fire stocks. Erich Pratt, the executive director of Gun Owners of America, called Trump's effort to ban the devices a "gross infringement of Second Amendment rights" while the Firearm Policy Coalition called the ban "lawless." Both groups are threatening legal action against any regulation that would ban the devices.

If a regulation effectively banning bump-fire stocks is implemented, it's hard to know what kind of impact it would have as there is no official count of how many of the devices are currently in civilian hands or how often they have been used in crimes. The bump-fire technique is possible even without the devices.