Russia is widening a crackdown on U.S. social media companies in an effort to assert more control over the information its citizens can access. 

After slowing the downloading of Twitter earlier this month, the country’s media watchdog, Roskomnadzor, on Tuesday threatened to block the service if it fails to remove questionable content.

“If Twitter doesn’t comply with Roskomnadzor’s demands, demands of the Russian legislation, then we’ll have to consider a full block across Russia,” said Vadim Subbotin, the agency’s deputy head, according to Russian news agency Interfax. 

Facebook, Instagram, and YouTube are also facing penalties, he noted.

This latest crackdown marks a new, more hostile stage of social media restriction in Vladimir Putin’s Russia, in which Moscow is looking to cement control over information and censor foreign social media. It comes after the arrest in January of Russian opposition leader Alexei Navalny, who had survived an assassination attempt by poisoning. 

Since then, Russia’s government has invited representatives of leading U.S. social media platforms for talks and issued new orders to remove content, particularly related to anti-government protests, child pornography, suicide, and drugs.

Last month the government singled out Twitter for failing to comply with its demands. Then on March 11 it slowed Twitter’s service, citing more than 3,100 posts that the company had not removed, including “child pornography, pro-drug, and suicide content,” according to an agency statement.

Russian authorities said it is now scrutinizing Twitter for posts dating back to 2017.

Twitter did not respond to a request by Fortune for comment.

Earlier this week, Russian authorities also told Google to remove age and other limitations on the film Rzhev: 500 Days Under Fire, a documentary about a World War II battle that is restricted by YouTube to viewers over 18. And on March 15, the government asked Instagram to reinstate the account of Crimea-24, a television channel dedicated to covering Crimea. The Instagram account was live as of Tuesday.

The regulator also held a “preventive conversation” with Paramount Pictures, the distributors of the TV show South Park, about “scenes that facilitate creation of social norms in society and intimate relations between adults and underage individuals.”

In addition to targeting social media, the Russian government introduced legislation last month authorizing new fines for companies that fail to follow censorship rules or restrict Russian media. Additionally, it plans to introduce legislation in April that would require domestic apps to come preloaded on foreign mobile devices sold in the country. That could reduce the revenue foreign tech companies earn in the Russian market, according to Russian business paper Kommersant. 

If implemented, these new measures could hurt Facebook, Google, Microsoft, and other U.S. companies in favor of Russian services like Yandex, Russia’s dominant search engine.

Not everyone is concerned about restricting freedom of information in Russia.

“I use VPN,” says Vyacheslav Gimadi, head of legal department at the Anti-Corruption Foundation (FBK) founded by Navalny. “I’m sure technically the government will not be successful; they’ve tried before with Telegram,” a messaging service launched by Russian-born entrepreneur Pavel Durov and a competitor to Facebook.

As the number of people protesting against the government in person has dwindled in recent months, censorship of social media platforms has become the main battlefield for Russians’ hearts and minds. 

While it may not be as popular as Russian-language platform VK.com or Instagram, YouTube is an important platform for disseminating independent content like Navalny’s recent viral investigation of Putin’s secret palace or the attempt against his life. 

“People use YouTube for a variety of things, including to access content that might not be shared on VK.com,” says Nina Jankowicz, a fellow at the public policy organization Wilson Center who focuses on disinformation and author of How to Lose the Information War: Russia, Fake News, and the Future of Conflict. “Ordinary people might be angry to have that cut off.”