Five Democratic lawmakers are attempting to push Google, Reddit and Twitter to ban the circulation of 3D-printed gun designs over their platforms.

Senator Dianne Feinstein of California and four others sent letters to the companies earlier this week, urging them to prevent their platforms from hosting any 3D-printed gun blueprints online. "Doing so will make all of our communities safer," the letters read.

The senators also addressed their letters to Craigslist, Yahoo, Microsoft, along with Facebook, the one company that has already begun banning the circulation of gun design files over its services.

The senators are calling for a crackdown amid a legal battle over whether circulating 3D-printed gun files should be legal in the US. Earlier this year, a gun rights activist named Cody Wilson won a settlement with the federal government that effectively allowed him to disseminate the files online, without fear of legal punishment. According to Wilson, his gun design blueprints are protected under free speech.

Nevertheless, several US state attorney generals are attempting to intervene on fears the files will pave the way for untraceable firearms. Last month, a coalition of states filed a lawsuit against Wilson and his company that won a court injunction preventing him from temporarily circulating the gun design files online. However, this hasn't stopped others from sharing their own 3D-printable gun files over the internet.

"There are already reports that thousands of such CAD (computer-aided design) files have already been downloaded by individuals, who can now disseminate the files privately or publicly on a variety of forums," the Democratic senators wrote in their letters to the internet firms.

The letters claim that banning the 3D-printed gun files fall under the companies' existing content policies, which forbid the solicitation of firearms and ammunition. Whether any of the affected companies decide to follow this interpretation is another matter. But Reddit told PCMag it recently decided to ban the 3D-printed gun files from the company's site with a change to its current content policy that was made on Wednesday.

"We are constantly reviewing our policies to ensure that they keep pace with new technological realities," a Reddit spokeswoman told PCMag. Prior to the policy change, the main 3D printing forum on Reddit already had rules against sharing information relating to firearm development.

Gun rights advocates are not happy about the crackdown. For instance, the Firearms Policy Coalition has accused Facebook of censorship for banning links to its own site, which carries a catalog of downloadable gun file designs, but for educational purposes. "How many people and pages have been banned for their pro-gun rights speech? Too many," the group claimed.

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