Moscow (CNN) -- Not backing down from their accusations that their country's parliamentary elections were rigged, thousands of Russian protesters planned a massive demonstration for Saturday.
The biggest rally is set for Moscow, but protests are slated for dozens of cities around the country.
The protesters are demanding an annulment of the results and a new vote.
United Russia, the party of Prime Minister Vladimir Putin, suffered big losses, but retained its majority in parliament.
Election officials on Friday released the official results: 238 seats for United Russia; 92 seats for the Communists; 64 seats for Fair Russia; and 56 seats for the Liberal Democrats.
Still, protesters say that these results are fraudulent.
Hundreds of protesters were arrested during demonstrations earlier this week.
Rally organizers and Moscow city officials agreed to allow demonstrators on Bolotnaya Square. The event is authorized to hold 30,000 people, yet tens of thousands more have indicated that they want to attend.
Organizers expect a large police presence as well, and they have urged protesters not to give the police any reason to shut them down.
"I believe it will be peaceful and a huge rally," said Boris Nemtsov, a former deputy prime minister and leading opposition figure.
He was among those arrested on Tuesday and was held for several hours.
"This is the first case where opposition is united," he said. "Which is great news. And very rare for Russia because mainly in Russia opposition is splintered."
Nemtsov believes that unity means public protests will now be a fixed part of Russia's political landscape as Putin campaigns to become president again early next year.
CNN's Alla Eshchenko contributed to this report.