No, a “stabilizing brace” is an accessory and ATF does not regulate accessories. However, a firearm equipped with a “stabilizing brace” may be subject to registration if it is a short-barreled rifle (SBR) because it is “designed, redesigned, made or remade, and intended to be fired from the shoulder,” as described by the amended definition of “rifle” in the Code of Federal Regulations and has a barrel(s) of less than 16 inches or an overall length of less than 26 inches.