The decision drew protests from the Prime Minister, Viktor Chernomyrdin, who condemned it as "ill-considered and harmful", and from Communists who predicted it was the forerunner in a Kremlin-inspired scheme to cancel the elections on 17 December.
The deputy chairman of the commission, Alexander Ivanchenko, suggested it might backtrack. It would reconsider the ban if ordered to by the Supreme Court.
In Washington, White House press secretary Mike McCurry said the commission's rulings were "a source of concern".
Even if the commission changes its mind, this will not eradicate suspicion the ban was a plot to destroy one of the most influential groups of liberal reformers. The commission is appointed by President Boris Yeltsin and is seen as a government tool. Yabloko is led by the economist Grigory Yavlinsky, who plans to run for the presidency next June.
The commission said it had rejected Yabloko's registration for the elections to the State Duma, or lower house, because it had dropped six candidateswithout proof of their consent, a minor breach of election law.
The chief proponent of the theory that the ban is a conspiracy is Mr Yavlinsky, who accused Kremlin hawks of using Mr Yeltsin's illness to sabotage his presidential bid. Others said if it was an act of skulduggery, it was ill-judged.
With Russians in a nationalist mood, Mr Yavlinsky is not a promising presidential candidate. Banning his party from the parliamentary elections is only likely to boost his popularity. A more plausible theory is that Yabloko was the victim of petty bureaucracy.
nPresident Yeltsin's health is improving after a heart problem but he will stay in hospital for at least three weeks, Itar-Tass news agency said yesterday.