A Russian court has imposed an 800,000 ruble ($14,000) fine on Telegram for refusing to provide the Federal Security Service (FSB) with encryption keys to the popular messaging app.
Judge Yulia Danilchik issued the ruling on October 16 at Moscow's Meshchansky District Court.
Telegram founder and CEO Pavel Durov called the FSB's demand an unconstitutional privacy infringement and said he was putting together a legal team to challenge the government's actions.
"The FSB's effort to get access to personal correspondence is an attempt to expand its influence at the expense of the constitutional rights of citizens," Durov wrote on VKontakte, the Russian-language social network that he founded.
He urged lawyers "who want to get involved" to contact Telegram and said the company would "pick a team with maximal experience in this sort of matter within a day or two."
Durov cited an article of the Russian Constitution that says every citizen has "the right to privacy of correspondence, telephone conversations, postal, telegraph, and other communications."
The ruling came after Durov said on September 27 that the FSB had notified him that his firm was in violation of counterterrorism laws requiring companies to provide access to encrypted communications they facilitate.
Durov posted scans of the FSB documents on VKontakte.
He said at the time that Russian authorities were pressuring Telegram to comply with controversial legislation known as the Yarovaya laws.
Rights groups call the laws a draconian infringement on privacy that can be used to stifle dissent, and Durov called them unconstitutional.
Durov launched Telegram with his brother in 2013. The messaging app has become an influential forum for news and debate, featuring popular channels run by news sites, journalists, and political analysts.
Asked on October 16 whether the Russian authorities would seek to block Telegram, President Vladimir Putin's spokesman said, "To my knowledge, this is not being discussed so far. In fact, no one has suggested it."
The spokesman, Dmitry Peskov, declined to comment on the court ruling.
In 2014, Durov announced that he had left Russia after he was forced to sell his stake in VKontakte amid pressure from authorities.