HARTFORD, Conn. (WTNH)– 3D-printer guns, commonly known as “ghost guns,” which can be plastic and invisible to metal detectors, are also untraceable because they lack a serial number.

Wednesday they were on the radar of gun safety advocates at the State Capitol.

“This is what we are dealing with. It has to be stopped in Connecticut and the rest of the country,” said Jeremy Stein, CT Against Gun Violence.

Flanked by orange and red t-shirt wearing members of anti-gun groups, Connecticut Attorney General William Tong announced the state will join 19 other states around the nation in a federal lawsuit against release of ghost gun blueprints.

Tong announced Connecticut is taking this legal action to protect Connecticut families. The lawsuit aims to block the Trump Administration from releasing the files to make ghost guns on the internet. Two years ago, a federal judge blocked this idea.

Under new proposed rules, the commerce department would regulate sharing of the blueprint files.

Gun safety advocates say it’s a loophole.

“The online availability of downloadable 3D guns gives the most technological people in our society – our children – easy access to something we are so desperately trying to keep out of their hands,” said Alexis Gevanter, Moms Demand Action.

Last year, Governor Ned Lamont signed a bill banning plastic ghost guns.

In Connecticut, you can print a homemade gun, but it must have metal in it and you have to register it with the state police.

Attorney General William Tong says “if you are for some reason a hobbyist, or want to produce a firearm at home, you must go to DESPP and serialize and register that firearm.”

The Connecticut Citizens Defense League, which represents 35,000 gun owners, is keeping a watchful eye on what happens next.

They said in a statement to News 8 Wednesday night:

“For most of our American history, firearms would have been considered ‘ghost guns’. In fact, the requirement for serialization only began in the last half century.

For generations, Americans have assembled and made guns often incorporating design improvements along the way. This is a part of American heritage.

So-called ‘ghost guns’ (3D printed firearms) are not accurate or reliable with the current available designs, nor can they function without metal components that includes ammunition.

The actual biggest source of firearms that are used illegally continue to be stolen or straw purchased guns which are already illegal.”

– Holly Sullivan, President- CCDL, Inc.

Thursday AG Tong released a statement announcing that a federal lawsuit has officially been filed “challenging the Trump Administration’s effort to allow online release of 3D-printed gun files.”