President Dmitry Medvedev on Wednesday signed a law that will give political parties larger representation in regional and municipal legislatures.
The amendments to the election law bans majority voting by requiring legislatures with 20 seats or more to distribute at least half the seats to those elected on party lists.
Previously, legislatures could be elected by majority vote, which gives more opportunities to independents, or by proportional vote, which favors parties, or a combination of both.
Medvedev, who announced the change in November, said it would build confidence in the party system. "It will develop trust toward the party system and raise parties' responsibility toward the voters," he said at the time.
But opposition parties warned on Wednesday that the change would give the ruling United Russia party a stronger foothold and violate voters' rights in a country where people often vote for specific candidates and their promises, not for parties.
The law limits voters' options, said Mikhail Matveyev, a Samara region lawmaker with the Communists.
"President Medvedev is interfering with local self-government, trying to change it into one that is governed from above," Matveyev said by telephone.
He said he feared the Kremlin wanted United Russia to gain more control of smaller legislatures.
United Russia swept this month's regional elections, the last big vote before State Duma polls in December, but by a less convincing margin than in previous years.
The law could help the opposition win extra seats in municipal elections but does nothing to address the "oppressive" problems of existing electoral legislation, said regional analyst Alexander Kynev.
Parties are currently prohibited from forming blocs, and public groups cannot nominate candidates for any elections. The State Duma vote also has a high entry threshold of 7 percent, which Medvedev said in 2009 should be lowered to 3 percent but has remained unchanged.
Any legislative changes are voided by the authorities' use of so-called administrative resources, said Galina Boldyreva, head of the Volgograd branch of the liberal Yabloko party.
But the new amendments will make it easier for the opposition to sue over foul play, she said.
The amendments also forbid lawmakers elected on a party's ticket from switching allegiances at the risk of their seats. Incumbents in municipal legislatures will also be spared from the cumbersome requirement of collecting signatures in support of their re-election bids.