3D printing firm MakerBot has removed blueprints for gun parts from its website, following last week's mass shooting in Sandy Hook.
In a letter to users from the company's lawyers, it explained that it now plans to enforce an existing clause in its terms of service.
Users of the company's Thingiverse site agree " not to collect, upload, transmit, display, or distribute any user content that... promotes illegal activities or contributes to the creation of weapons, illegal materials or is otherwise objectionable".
The blueprints removed include parts for the AR-15, the assault rifle used by Adam Lanza to shoot 20 first graders last week.
The exact same gun is the subject of the Wiki Weapon Project, organized by a collective called Defense Distributed. Its first prototype broke after firing six rounds.
And the group had another big setback in October, when 3D printer manufacturer Stratasys revoked the group's license and took its printer back.
Even before last week's shooting, the possibility of 3D printed guns was raising concern. Earlier this month, Congressman Steve Israel announced legislation to renew a ban on plastic guns that is set to expire next year.
"Congress passed a law banning plastic guns for two decades, when they were just a movie fantasy. With the advent of 3D printers, these guns are suddenly a real possibility, but the law Congress passed is set to expire next year," he says.
"We should act now to give law enforcement authorities the power to stop the development of these weapons before they are as easy to come by as a Google search."
His act would make it illegal to manufacture, own, transport, buy or sell any firearm that can't be detected by a metal detector or seen clearly by an X-ray machine.