Analysts have said unification is one solution to the current funk Russia's liberal parties are in. New regulations for next year's parliamentary elections have made it less likely that either Yabloko or the SPS will get any seats in the Duma.
"Yabloko does not regard the SPS as an equal partner and is not ready to unite with the SPS on an equal footing, Nikita Belykh told a party congress.
He said Yabloko is not prepared to change its name or program.
"Such conditions are unacceptable for us," he said.
Belykh also said he is ready to resign if his party loses the March 2007 regional elections.
Belykh said earlier the SPS will form an opposition faction if it succeeds in the 2007 elections, and will make every effort to become Russia's ruling party in 2015.
"In 2011 we intend to increase our representation [in the Duma] and form an influential grouping to block draft bills which are not in line with the principles of democracy and a market economy," he said. "In 2015, we intend to be a ruling party."
The SPS, which supports western-style capitalism and is associated with the free market reforms and privatization of the 1990s under the presidency of Boris Yeltsin, failed to reach the 5% threshold in the 2003 elections needed to take up seats in the lower house of parliament, the State Duma. It has two seats in the 450-seat Duma, all from single-mandate districts, compared with the 32 it took in 1999.
In 2003, Yabloko won only four seats and the SPS three in Russia's 450-seat Duma, and all from single-mandate districts as both parties won less than the 5% of the vote necessary to get deputies elected from party lists.