Thousands of people marched through Moscow, throwing paper planes and calling for authorities to unblock the popular Telegram instant messaging app on Monday.
Protesters chanted slogans against President Vladimir Putin as they launched the planes - a reference to the app's logo.
"Putin's regime has declared war on the internet, has declared war on free society... so we have to be here in support of Telegram," one protester told Reuters.
Russia began blocking Telegram on April 16 after the app refused to comply with a court order to grant state security services access to its users' encrypted messages.
Russia's FSB Federal Security service has said it needs access to some of those messages for its work, that includes guarding against militant attacks.
In the process of blocking the app, state watchdog Roskomnadzor also cut off access to a slew of other websites.
Telegram's founder, Russian entrepreneur Pavel Durov, called for "digital resistance" in response to the decision and promised to fund anyone developing proxies and VPNs to dodge the block.
More than 12,000 people joined the march on Monday, said White Counter, a volunteer group that counts people at protests.
"Thousands of young and progressive people are currently protesting in Moscow in defense of internet freedom," Telegram's Durov wrote on his social media page.
"This is unprecedented. I am proud to have been born in the same country as you. Your energy changes the world," Durov wrote.
Telegram has more than 200 million global users and is ranked as the world's ninth most popular mobile messaging service.
Iran's judiciary has also banned the app to protect national security, Iranian state TV reported on Monday.