a sign hanging off the side of a building: Key Speakers At Dmexco Digital Marketing Conference Key Speakers At Dmexco Digital Marketing Conference

The U.S. technology companies “have caved into the Kremlin’s blackmail,” Leonid Volkov, a top aide to jailed opposition leader Alexey Navalny wrote on Telegram. The Putin critic’s supporters denounced the move as “a shameful act of political censorship.” Apple and Google didn’t immediately respond to requests for comment.

Russian authorities had accused the companies of meddling in the elections by offering the opposition app despite court rulings banning access to the content. Legislators said the companies’ staff could face criminal charges if the apps weren’t removed, Russian news agencies reported. Regulators threatened new fines and other measures.

Navalny’s so-called smart voting initiative aims to concentrate popular discontent to defeat ruling party candidates; Russian courts have banned mention of it online. Russia is holding three days of voting for the State Duma lower house of parliament from Friday to Sunday, in which Putin’s unpopular United Russia party is counting on a commanding victory.

The crackdown also led to interruptions in access to Google Docs in Russia after Navalny’s supporters used the text editor to distribute its lists of recommended candidates, according to Roskomsvoboda, an Internet advocacy group. Similar problems were reported earlier in the week with Apple’s App Store, through which the smart voting app was distributed.

President Vladimir Putin, 68, after two decades in power has sharply stepped up efforts to rein in the internet, which has remained a bastion of free speech. Earlier this year after mass protests at Navalny’s imprisonment, Russia slowed down access to Twitter. It also slapped fines of several million dollars on social media companies including Facebook and Google for not deleting calls for demonstrations that were ruled illegal by authorities.