Russia's election officials have barred former Prime Minister Mikhail Kasyanov from running as an opposition candidate in the March presidential election.
Kasyanov says the authorities are afraid of the political contest
The Central Election Commission (CEC) said there were many invalid signatures in Mr Kasyanov's list of supporters.
Mr Kasyanov served under President Vladimir Putin, but has become one of his staunchest critics. He called on Russians to boycott "this farce".
Mr Putin's chosen successor, Dmitry Medvedev, is expected to win in March.
Russian law stipulates that no more than 5% of signatures in support of a candidate can be false or forged.
In Mr Kasyanov's case, 13.36% were rejected, the CEC announced. The decision was unanimous.
In a statement, Mr Kasyanov said: "There is no doubt that the decision not to register my candidacy was taken personally by Vladimir Putin."
"The country has finally gone on the slippery slope to totalitarianism."
The CEC has registered three other candidates apart from Mr Medvedev - Gennadiy Zyuganov, Vladimir Zhirinovsky and Andrey Bogdanov.
Dmitry Medvedev, who is chairman of the gas giant Gazprom, has been leading recent opinion polls.
Mr Kasyanov, who would have been the only liberal running for the presidency, has been polling about 1%.
He says all this is part of a deliberate campaign by the Kremlin to crush his political ambitions.
And he has complained that his staff, including those who had to collect all the signatures from around the country, have been subject to a massive campaign of intimidation.
Although Mr Kasyanov stood absolutely no chance of winning the election, the Kremlin may have feared he could use the election campaign to criticise President Putin's record in office, says the BBC's Richard Galpin in Moscow.
And criticism is something the Kremlin seems increasingly unwilling to tolerate, our correspondent says.