Eight states and Washington, D.C., are suing the Trump administration for allowing a Texas man to distribute instructions on how to make printable three-dimensional guns.
The technology would allow people to manufacture weapons in their own homes.
Washington state Attorney General Bob Ferguson is leading the lawsuit and said he has a question for the administration.
"Why are you allowing dangerous criminals easy access to weapons? These downloadable guns are unregistered and very difficult to detect, even with metal detectors, and will be available to anyone regardless of age, mental health or criminal history."
On Twitter Tuesday, President Donald Trump said he is looking into the issue. "I am looking into 3-D Plastic Guns being sold to the public. Already spoke to NRA, doesn’t seem to make much sense!," he said.
I am looking into 3-D Plastic Guns being sold to the public. Already spoke to NRA, doesn’t seem to make much sense!— Donald J. Trump (@realDonaldTrump) July 31, 2018
The blueprints created by a Texas company allow anyone with a 3-D printer to make the parts for a plastic gun that would cost just a few hundred dollars.
The State Department had ordered militant Texas gun rights advocate Cody Wilson to stop distributing the blueprints, arguing they violated U.S. export laws.
Wilson sued, alleging that the ban violates his constitutional rights, and the Trump administration reversed itself.
The lawsuit by the eight states and the District of Columbia say allowing people to make their own plastic guns violates state controls over weapons.
But gun experts say the plastic handguns may not work without certain metal parts, and also have a tendency to blow up and break apart in users' hands.
They also say the 3-D printer needed to make the guns is expensive.