The United Russia-dominated Moscow City Duma signed off on legislation Wednesday that will drastically reduce opposition parties' chances of winning seats in the legislature.

The bill introduces a rare, controversial method to distribute seats called Imperiali, which provides a disproportionate number of seats to election winners.

The Duma approved the amendment to Moscow's Election Code in a vote of 29 to 6, with all United Russia deputies supporting it and the Communist Party and Yabloko opposing it, Duma spokesman Nikolai Figurovsky said.

The current system gives each party a number of seats that is proportional to the number of votes it garnered in elections. It requires parties to collect at least 7 percent of the vote to get seats.

Under the Imperiali system, the winning party would get one or two additional seats at the expense of the losing party. The system would apply to the party list vote, not single-mandate candidates. The 7 percent barrier would remain.

"It is a method that allows United Russia to steal two seats from the other two parties," Yabloko leader Sergei Mitrokhin told The Moscow Times.

In the current City Duma, 29 seats belong to United Russia, four to the Communists and two to Yabloko.

But Ivan Novitsky, a City Duma deputy with United Russia, said the Imperiali method would provide a "more precise way of counting the vote."

Lilia Shibanova, head of Golos, an independent group that monitors elections, said one or two extra seats would give a "considerable advantage" to the winning party given the relatively small number of seats in the City Duma.

United Russia fears that public support might shrink amid the crisis and is using "any opportunity to get one or two extra seats for itself," said Alexander Kynev, an independent elections analyst. Kynev noted that the Imperiali formula is used "practically nowhere" else in the world.

A Belgian clerical and rightist political activist invented the Imperiali formula in 1921 as a way to push leftist and secular politicians out of municipal elected bodies. The Imperiali system is used in national elections in Italy and in local elections in Belgium. Belgium, however, is drafting legislation to scrap the Imperiali method.

The Imperiali system was first tested in Russia in March 2007 elections in St. Petersburg and the Moscow and Samara regions. A method similar to Imperiali that gives fewer extra seats to the winning party was used in the Tyumen region. The Imperiali method was used in six regions in elections this March.

Mitrokhin, of Yabloko, said the Imperiali method "contradicts" federal law because it "doesn't provide for the proportional representation of a party" in a legislature.

But Vladimir Lakeyev, the head of the Communist faction in the City Duma, noted that the Supreme Court ruled in July 2007 that the Imperiali method was legal.

Lakeyev complained about the haste with which he said the legislation was passed Wednesday. He said deputies were given only half an hour to read it, and it was "impossible to understand complex mathematic calculations" in such a short time.

The next City Duma elections will take place in October, according to the City Duma's web site.