All stems from the fact that FSB, Russia's main intelligence service, had previously requested access to Telegram encryption keys so it could access encrypted messages sent through the app.
All of this started a year ago when the FSB, the successor to the KGB, demanded that the founder, Pavel Durov, hand over encryption keys to the service. That April 4 deadline has now passed, and the company still hasn't handed over the keys, claiming that doing so would be a violation of user privacy.
Russia's Roskomnadzor communications watchdog said it had filed a lawsuit at a Moscow court on Friday "with a request to restrict access on the territory of Russian Federation to the information resources of".
Russia's main security agency, the FSB, wants the keys so it can read messages and prevent future terror attacks in the country.
Ranked as the world's ninth most popular mobile messaging app, Telegram is widely used in countries across the former Soviet Union and Middle East.
Telegram says it can not comply with this demand because it employs end-to-end encryption.
Telegram's lawyer Pavel Chikov last month said: "The FSB's argument that encryption keys can't be considered private information defended by the Constitution is cunning".
It's also worth noting that if a block is indeed put in place, users of the app could still quite easily utilize the in-built proxy features of the app to circumvent it, making any potential blocking of the app very hard. Trying to fight Russian pressure, Telegram filed a lawsuit against the Russian government at the European Court of Human Rights (ECHR).
The Kremlin considers Telegram as a convenient messenger and uses it, including in communications with journalists, Kremlin spokesman Dmitry Peskov told a daily briefing.
Telegram's self-exiled Russian founder Pavel Durov has long said he will reject any attempt by the country's security services to gain backdoor access to the app.