The social-networking site Facebook, and its Instagram photo-sharing service, are prohibiting person-to-person firearms transactions and related firearms advertising on the popular platforms.

The Friday move comes almost a month after President Barack Obama announced an executive initiative requiring those selling guns—whether at a flea market or online—to register as a firearms dealer and to perform background checks on gun purchasers. The White House has urged Silicon Valley to bake encryption backdoors into its wares, and has also urged social media companies to make it difficult for unlicensed gun dealers to sell firearms on their networks. Silicon Valley, however, has publicly balked at calls for encryption backdoors. Facebook's changeover is part of its updated terms of service that also prohibit its 1.6 billion monthly visitors from selling marijuana, pharmaceuticals and illegal drugs.

The company will remove posts reported by its users that violate the policy, which had already prohibited firearms sellers from promoting "no background checks required." Licensed dealers, which by law must perform background checks, may still advertise as long as transactions occur outside Facebook properties. Minors have already been shielded from seeing pages advertising guns. Repeat violators of Facebook's policy, designed to clamp down on unregulated gun sales, could be banned from the social network.

Monika Bickert, Facebook's head of product policy, said in a statement that "Over the last two years, more and more people have been using Facebook to discover products and to buy and sell things to one another. We are continuing to develop, test, and launch new products to make this experience even better for people and are updating our regulated goods policies to reflect this evolution."

After a string of mass shootings nationwide, the president declared that "Anybody in the business of selling firearms must get a license and conduct background checks or be subject to criminal prosecutions."

The president's executive action has been met with a federal lawsuit (PDF) targeting the Obama administration.

"It is clearly arbitrary and capricious for the defendants, each and every one of them, to now suddenly adopt and implement a new and different interpretation for no other reason than the political preferences of temporary occupants of elected office," according to the lawsuit by Larry Klayman, the founder of Freedom Watch.