Russia's communication watchdog said on Monday it was opening administrative proceedings against Twitter and Facebook for failing to explain how they plan to comply with local data laws, the Interfax news agency reported.
Roskomnadzor, the watchdog, was quoted as saying that Twitter and Facebook had not explained how and when they would comply with legislation that requires all servers used to store Russians' personal data to be located in Russia.
The agency's head, Alexander Zharov, was quoted as saying the companies have a month to provide information or else action would be taken against them.
Russia has introduced tougher internet laws in the last five years, requiring search engines to delete some search results, messaging services to share encryption keys with security services and social networks to store Russian users' personal data on servers within the country.
At the moment, the only tools Russia has to enforce its data rules are fines that typically only come to a few thousand dollars or blocking the offending online services, which is an option fraught with technical difficulties.
However, sources in November told Reuters that Moscow plans to impose stiffer fines on technology firms that fail to comply with Russian laws.