The 25-year-old ban on firearms that can't be detected by metal detectors is set to expire in December, and Attorney General Eric Holder is concerned that the 3-D printing technology could lead to a vast increase in the number of metal-free guns being smuggled into and out of the country.

"This is a very worrisome threat to law enforcement and to people who fly every day. We can't have guns legally in circulation that are not detectable by metal detectors," Holder said in a statement.

"Whatever people’s feelings are about gun-safety legislation, this is something we should all agree needs to be reauthorized."

The 1988 Undetectable Firearms Act is scheduled to expire on December 9th. It requires that all guns -- even plastic ones -- contain at least one metal element that can be detected by existing detection technology.

Proposals to renew the act have been submitted Bill Nelson, a Democrat in the Senate, and Steve Israel, a New York Democrat, but neither proposal has gained traction.

One of the owners of Defense Distributed, a group that aims to "democratize firearms manufacturing," responded to Israel's proposed legislation earlier this year, wishing the representative "good f*cking luck" in getting it passed.

["Man With A Gun, Isolated On A White Background" on Shutterstock]