The designs were not due to be made public until Wednesday, following a ruling from the US Justice Department.
But blueprints for nine types of gun were uploaded to the Defense Distributed website on Friday.
And, on Monday, multi-state legal action was filed seeking to block the ruling that Americans could see them.
President Trump has also voiced concern via his Twitter account.
I am looking into 3-D Plastic Guns being sold to the public. Already spoke to NRA, doesn't seem to make much sense!