Protesters have converged on a court in Moscow after an opposition activist had his prison term extended.
Sergei Udaltsov went on hunger strike after being arrested earlier this month for staging a rally without approval.
Just as he was due to be released at the weekend, the court prolonged his prison term for resisting the police at a separate protest in October.
“We are here to defend the rights of one man, Sergei Udaltsov. He’s been on hunger strike for the last two weeks and has already spent a whole month, for nothing, behind bars,” said Garry Kasparov, leader of the Solidarity opposition party.
Udaltsov has been arrested at least 14 times this year and spent at least 50 days in prison.
His supporters say that due to the hunger strike, his state of health is giving them cause for concern.
The Kremlin is already dealing with widespread anger over the disputed parliamentary election on December 4.
The focus of much of that anger, Vladimir Putin, is hoping to be elected president in March.