Wikipedia shut down its Russian-language site for 24 hours to protest against a Bill that would give the Russian government sweeping powers to blacklist certain sites.
The Bill is the latest in a flurry of legislation that appears aimed at neutering a growing opposition movement that has protested against president Vladimir Putin's rule.
Politicians say the Bill, which is to be reviewed in parliament, is designed to protect children.
Supporters say it enables the government to block sites that show child pornography, promote teen suicide, or spread information about drugs. But critics argue it gives too wide a scope for the government to subjectively select which sites to blacklist.
The Kremlin has made no public comment on the Bill, but politicians from Mr Putin's party were among those who wrote the legislation, and it is likely to pass. It follows other recent laws that have targeted groups Mr Putin views as rivals or bad influences: a law imposing heavy fines for protesters was quickly pushed through parliament in June, and a Bill that would label NGOs receiving foreign aid as "foreign agents" was approved last week.
Russia's internet has until now been relatively unrestrained by government restrictions or firewalls. While anti-government activists or media have often been the victims of hacking attempts in recent years, the government has largely left the internet an unregulated space for political discussion.
So the new Bill has provoked a flurry of protest online, with many expressing support for Wikipedia's actions. Three of the top Twitter hash tags in Russia were RuWikiBlackout, Wikipedia and Law No. 89417-6, all of which refer to the legislation. Human rights activists and opposition leaders also loudly criticised the Bill. The Presidential Council of Human Rights urged parliament not to pass the legislation in its current state.
Others were more sceptical about the actual restrictive power of the law, asserting that it was designed to test the Russian public's reaction and serve as a warning against anti-government activity online. Anton Nossik, media director of internet holding company SUP, which runs Russia's most popular blogging platform, wrote that there "won't be any immediate consequences if this law is passed". But, he added, "the reality is that they are testing to see how to adopt such measures in the future ... For the past 12 years I was sure that the Russian government was smart enough not to censor the internet. Now they are scattering any doubt that Russia is on the path of government regulation that is senseless and ruthless", he wrote.
Russians in large cities have become accustomed to unfettered access to the internet. In an AP-GfK poll released in June, only 10% of those polled in Moscow said they did not use the internet. Internet use throughout the country is on the rise, with 38% of Russians now using the internet daily, up from 22% just two years ago, according to the Public Opinion Foundation.
Wikipedia's Russian-language site encouraged users to spread the word about the law and contact their representatives in parliament to lobby against it. The protest comes after a similar shutdown of the English-language site in January to protest against the anti-pirating Stop Online Piracy Act in the US Congress.