A federal judge on Tuesday blocked a Texas company from releasing instructions on how to use a three-dimensional printer to make guns at home.
Judge Robert Lasnik issued his restraining order from Seattle just hours before gun rights advocate Cody Wilson was to have started putting the blueprints on the internet.
"There is a possibility of irreparable harm because of the way these guns can be made," the judge wrote.
Attorneys general from nine states and the District of Columbia had filed a lawsuit in Seattle against the Trump administration to try to prevent the gun plans from being distributed.
They said downloadable guns would be unregistered and very difficult to detect and also would be available to anyone regardless of age, mental health or criminal history.
The blueprints created by the company, Defense Distributed, would 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 Cody Wilson to stop distributing the blueprints, arguing they violated U.S. export laws.
Wilson sued, alleging the ban violated his constitutional rights. The Trump administration reversed itself and said Wilson could again start publishing the gun plans starting Wednesday. That decision is now on hold.
But it is unclear how many people got copies of the plans before the State Department ordered Wilson to stop.
Doesn't 'make much sense'
On Tuesday, Trump himself questioned the wisdom of allowing people to assemble homemade weapons.
"I am looking into 3-D plastic guns being sold to the public. Already spoke to the NRA, doesn't seem to make much sense," Trump tweeted.
Some senators want Trump to do more than tweet and talk to the National Rifle Association. Several Democrats introduced a bill Tuesday that would outlaw the dissemination on the internet of blueprints for plastic homemade guns.
Senator Ed Markey, a Massachusetts Democrat, appealed to Trump to fix what he called a "deadly mistake" his administration made.
"Donald Trump will be totally responsible for every downloadable plastic AR-15 gun that will be roaming the streets of our country," he said.
Connecticut Democratic Senator Richard Blumenthal put it more bluntly, saying if the president did not stop plastic guns, "blood is going to be on his hands."
Gun experts say the plastic handguns may not work without certain metal parts, and that the guns also have a tendency to blow up and break apart in users' hands.
The experts also say the 3-D printer required to make the guns is expensive.