Cody Wilson, director of Defense Distributed, said it is his constitutional right to post the files online.
The federal government settled a lawsuit with Wilson's organization Defense Distributed, allowing the company to publish its first batch of blueprints last Friday.
"Even Congress can't ban 3D printers, the internet, or the 1st Amendment", Kentucky Republican Rep. Thomas Massie tweeted on Tuesday.
Supporters, meanwhile, tout 3-D printing technology as a way to skirt what they view as stringent government regulation of firearms.
"People have been making guns at home for personal use for ages, plastic (not undetectable, still uses metal) or not". Pennsylvania Attorney General Josh Shapiro went to court to temporarily block the group's Web site within his state. And he blames the Trump administration for letting them happen.
As uproar mounted Tuesday, the White House expressed scepticism over the legality of Wilson's efforts - even though the administration had given the green-light for the project.
A 3-D printed gun's quality often depends on the sophistication of the printer and the quality of the plastic used.
Trump tweeted that he has already spoken with the National Rifle Association about the downloadable directions a Texas company wants to provide for people to make 3D-printed guns.
Assembling your own gun is legal, according to the Bureau of Alcohol, Tobacco, Firearms and Explosives, provided you don't sell it. "The administration supports this almost two-decade old law". In June, the government entered into what it called a voluntary settlement of the case after negotiations, and agreed to pay almost $40,000 of Wilson's legal costs. Eight states have filed suit to block the decision, contending that the plastic weapons are a boon to terrorists and criminals and threaten public safety.
"I intend to litigate", he told the magazine. "Gun blue prints are and have always been readily available on the internet", he tweeted.
A reporter was able to download two files from the website on Tuesday, though it had some technical glitches and was hard to access. In addition to granting Wilson permission to publicly release the files online, the government also agreed "to pay almost $40,000" in legal fees for Wilson, according to The New York Times.
But federal courts have disagreed. "Yet that's exactly what the Trump administration is allowing".
Kerry Stevenson, editor and founder of the 3D printing blog Fabbaloo, said the level of alarm over the release of the 3D-printed gun designs is unwarranted.
Earlier in July, Los Angeles police showcased an arsenal of such weapons, using some home-made parts, seized from gang members during a six-month undercover operation. Wilson's website also features blueprints for the AR-15.
In the lawsuit filed Monday, the attorneys general claimed that the settlement's "temporary modification" violated the Administrative Procedure Act, which requires a period for public comment and congressional notification for category transfers.
Michael Guslick's homemade pistol combines plastic and metal parts to create a functional weapon. "We will not be silenced", Wilson posted on Twitter. "These ghost guns are the new wave of American gun violence".
States are free to enact gun control measures, but 'what they can't do is censor the speech of another citizen in another state, and they can't regulate the commerce of another citizen in another state when that commerce is authorized by a federal government license, ' Blackman said in an interview Monday.