Representative Steve Israel (D-NY) plans to introduce a bill which will ban the use of 3-D printers to make firearms that are actually or even potentially undetectable.
According to Guns.com, Israel is chiefly concerned about The Liberator–the first truly “printable handgun designed by Defense Distributed.” Although the gun contains metal which prevents it from being undetectable, Israel believes the gun provides an option for terrorists who could remove the metal, and thereafter be in possession of a gun that could pass through metal detectors.
Note the way Israel is approaching this–although the gun contains metal and is therefore detectable and in compliance with law, he wants to further regulate the manufacture of the gun on the grounds that a non-law-abiding citizen might alter it–remove the metal–and misuse it.
In other words, Israel wants to punish law-abiding citizens for the possible criminal or terror-related behavior of others.
CBS News reports that other Democrats tried to do this same thing in December 2013, when Congress renewed the Undetectable Firearms Act (UFA). That act, first passed in 1988, bans the manufacture of undetectable guns, period. Yet during the renewal of the law, certain Democrats pushed to broaden it, so as to increase the amount of metal that every 3-D printed gun would have to contain.