Telegram’s battle with Russia’s authorities took a new turn today when state communications regulator Roskomnadzor started legal action aimed at limiting access to the app within the country.

As part of a so-called anti-terrorist bill proposed in 2016, Russian agencies such as the Federal Security Service (FSB) would be allowed access to encrypted messaging services, letting them search through user data.

Last year, the FSB demanded Telegram share its encryption keys, but the company refused and was hit with a $14,000 fine. Last month, Supreme Court Judge Alla Nazarova rejected Telegram’s appeal against the penalty and upheld the order.

Roskomnadzor said Telegram had 15 days to comply with its demands. 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. According to the BBC, the company said that the way the service is built means it can’t even access them.

Roskomnadzor has filed a lawsuit at Moscow court today “with a request to restrict access on the territory of Russia to the information resources of ... Telegram Messenger Limited Liability Partnership.”

Telegram’s lawyer, Pavel Chikov, criticized the move, calling it “groundless.”

"The FSB's requirements to provide access to private conversations of users are unconstitutional, baseless, which cannot be fulfilled technically and legally,” he said, in a statement.

Telegram is the ninth-most-popular messaging app in the world, boasting over 200 million active users. It has a focus on privacy and encryption and is especially popular in locations such as the middle-east and Russia.