The Bureau of Alcohol, Tobacco, Firearms and Explosives has published a notice outlining their plans to update regulations on stabilizing braces.

Originally developed to help those with disabilities shoot comfortably, stabilizing braces have become a popular firearm accessory used to legally adapt AR-style pistols into guns that can be shot from the shoulder, like the highly regulated short-barreled rifle.

According to the ATF, stabilizing braces will now have to conform to a set of stringent guidelines to be considered legal. If they don't meet those standards, they—and the gun to which they're attached—will automatically become regulated as a rifle under the National Firearms Act.