SPS leader Nikita Belykh said his party would go to the Constitutional Court to challenge rules that curb voters' freedom of choice.
Andrei Kosmynin, a spokesman for the liberal Yabloko party, said his party was considering a similar move.
Russia's Democratic Development
Demonstrators speak with local politicians in Butovo about the destruction of a local forest in July 2006 (RFE/RL)
IS RUSSIAN DEMOCRACY MANAGING? Russian President Vladimir Putin has said Western powers seek to pressure Russia under the pretext of concern over its democratic development. He has said Russia is ready to listen to "well-intentioned criticism," but will not allow anyone to interfere in its internal affairs. The Kremlin has been criticized for stifling political oppostion, increasing central control over the media, and cracking down on the work on nongovernmental organizations.