Russia's communications regulator has said that it will soon check whether Facebook is complying with a Russian law requiring social networks to store the personal data of Russian citizens on Russian servers.
Roskomnadzor has repeatedly warned Facebook and other social networks that they could be banned next year unless they comply with the law.
"In the near future Roskomnadzor will plan a series of supervisory activities aimed at analyzing the activities of the administration of Facebook in terms of the processing of Russian users' personal information," it said in a statement carried by the Russian news agency Interfax on November 8.
Russian authorities say the law, introduced in 2014, is aimed at protecting Russians' personal data.
Critics, however, see it as an attempt to tighten control over social-media networks that have been particularly popular with Russian opposition activists.
Last year, Roskomnadzor blocked access to LinkedIn to comply with a court ruling that found the networking service guilty of violating the same data-storage law.
LinkedIn has yet to come to an agreement with Russian authorities to restore public access to the service.
Roskomnadzor said on November 8 that Twitter had agreed to comply with the storage law. Twitter did not comment on the assertion, however, and AFP quoted an anonymous source as saying that Twitter was still reviewing the matter.
The AFP source said that Twitter wanted to ensure that using storage sites in Russia "does not create a security risk or any vulnerability for Russian users and their accounts."
Last month, Twitter banned advertisements from Russia's state-controlled RT and Sputnik media outlets in response to U.S. intelligence findings that they sought to spread misinformation during the 2016 presidential election.
Facebook has also taken steps to banish ads and posts placed by Russian operatives on its U.S. network.