One of Russia's leading liberal political parties, Yabloko, has been banned from local elections in the second biggest city, St Petersburg.
Yabloko has lost most of its influence in recent years
The city's electoral commission said too many signatures supporting the party's candidates had been invalid.
Yabloko said the commission's decision was an attempt to muzzle the voice of the opposition to the pro-Kremlin municipal council.
It said it would appeal. The elections are due to be held on 11 March.
St Petersburg's electoral commission said nearly 12% of signatures backing Yabloko's candidates had been declared invalid - more than the maximum 10% allowed.
"This provides grounds for refusing to register the Yabloko list," the commission's deputy head Dmitriy Krasnyanskiy was quoted as saying by Russia's Interfax news agency.
Yabloko said the move was politically-motivated.
"The electoral commission took revenge on us because we are in opposition to the authorities," the head of Yabloko's branch in St Petersburg told Reuters news agency.
Yabloko has lost most of its influence since Vladimir Putin became president in 2000.
The municipal elections in Russia are seen by some analysts as a rehearsal for parliamentary polls in December.