Authored by Tom Ozimek via The Epoch Times (emphasis ours),

The Biden administration has dialed up its crackdown on so-called "ghost guns" by issuing guidance that basically expands the definition of what "readily converted" means in a new federal rule and making more do-it-yourself pistol parts subject to restrictions.

In an open letter to firearms dealers (pdf) dated Dec. 27, the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) told firearm vendors that nearly-complete handgun frames or receivers—basically the pistol grip and firing mechanism—will be treated the same as fully completed firearms.

Ghost Gun Rule

Firearm vendors who sell near-complete pistol frames and receivers—often as kits that can be relatively easily turned into untraceable homemade guns—were hit with the new rule in August, which required that frames and receivers that could be "readily converted" into fully operational guns are subject to the same regulations as traditional firearms.