Russia on Thursday blocked LinkedIn on charges that the company was storing personal data of Russian citizens on its US server.

Roskomnadzor, Russia’s communications regulator, said it was acting to protect Russian Internet users’ data, Reuters reported on Friday. Russian law requires websites which store the personal data of Russian citizens to do so on Russian servers, something it said LinkedIn did not do.

All Internet service providers were asked to block public access to the website of LinkedIn to comply with a court ruling that found the firm guilty of violating data laws.

LinkedIn, headquartered in the United States, has more than 6 million registered users in Russia. It is the first major social network to be blocked by Russian authorities.

LinkedIn’s site would become unavailable in Russia within a day, the Interfax news agency cited Roskomnadzor spokesperson Vadim Ampelonsky as saying. One Internet service provider, Rostelcom, said it had already blocked access to the site.

In a statement earlier this month LinkedIn had said that the decision risked denying access to its site for millions of Russian members, including companies, who use it to grow their businesses.

The law requiring websites which store the personal data of Russian citizens do so on Russian servers was introduced in 2014, but never previously enforced.

Critics see the move against LinkedIn as part of an attack on social networks in a country which has increasingly tightened control over the Internet in recent years.