Not content with letting social media sites police content on their own, five Democratic U.S. Senators have sent letters to the heads of major tech companies urging them to “proactively” block users from accessing blueprints for 3-D printed guns.

The U.S. government recently settled with Defense Distributed, a website that allowed users to download the blueprints for 3-D printed guns. A federal judge later blocked the release of the blueprints online. Because the order is only temporary, Sens. Dianne Feinstein (D-CA), Bill Nelson (D-FL), Bob Menendez (D-NJ), Richard Blumenthal (D-CT) and Ed Markey (D-MA) all signed onto letters encouraging Facebook, Twitter, Google, Microsoft, Reddit, Yahoo, and Craigslist to crackdown on users who may be sharing files that would allow users with access to a 3-D printer to print guns.

The letters, which are available on Feinstein’s website , plead with the tech giants to use their terms of service in order to “proactively” prohibit users from freely sharing the files. The letters refer to specific portions of the sites’ respective terms of service which could, in theory, be applied to ban users from sharing the blueprints.

The Twitter letter, for instance, says, “We appreciate that your company, like other social media companies, has terms of service that allow Twitter to remove content like 3-D gun designs from its platforms” before referencing the Twitter’s terms of service, the Twitter Rules, and the prohibition on glorifying violence.

“Based on your own terms of service, we urge you to proactively prevent the online dissemination of these dangerous 3-D designs across all of your platforms. Doing so will make all of our communities safer,” each letter ends.