MOSCOW – A prominent opposition activist was stripped of his seat in the lower house of the Russian parliament on Friday, a move that heightens concerns that the Kremlin will continue an aggressive crackdown on political dissent.

Gennady Gudkov, 52, a protest movement leader and member of the opposition Just Russia party, was expelled by a 294-151 vote of the State Duma, controlled by President Vladimir Putin’s United Russia party. Gudkov, once an ally of Putin, called the action political vengeance by the Kremlin.

“You are trying by repressions to shut up the mouths of the opposition and to stifle the critics,” Gudkov, a former KGB officer and then a successful businessman, told Duma members prior to the vote. “What are you doing to the country? Where are you leading the Russian people?”

The vote came on the eve of an opposition mass demonstration, the first large-scale anti-Putin protest to be held in downtown Moscow after a long summer break.

Since Putin’s first term as president more than a decade ago, several lawmakers have been stripped of their parliamentarian immunity. Gudkov, however, became the first Russian legislator who lost his job for allegedly mixing his parliamentarian duties with business. Prosecutors who appeared before the Duma on Friday displayed a photocopy of a document from Gudkov’s former company dated last July that allegedly contained his signature. Gudkov called it a fake.