Russia's Supreme Court on Monday decided to exclude the liberal opposition Yabloko party from September's parliamentary election, citing alleged breaches of electoral law.
Presiding Judge Vyacheslav Kirillov followed a request by the prosecution to bar Yabloko, a party that has campaigned for an end to the war in Ukraine, from participating in the vote.
The lawsuit was brought by the nationalist pro-Kremlin Rodina (Motherland) party, which had complained about a number of alleged violations of electoral law in the registration process after the electoral commission granted the opposition party surprise permission to participate in July.
Yabloko tried to fend off the allegations during an hours-long hearing on Monday, while hundreds of its supporters gathered outside the courtroom.
The party has said it will appeal the ruling.
Rodina accuses Yabloko of violating copyrights in its campaign materials, for example by depicting doves of peace, and of spending an impermissibly large amount of money on online advertising.
The party has also been accused of having received 16,900 roubles (around $205) in campaign funding from the US and Germany.
Yabloko's lawyers have rejected the allegations.
Yabloko leader Nikolai Rybakov said in his closing statement that his party had committed no legal violations, stressing that Yabloko stood for peace, freedom and a life without fear.
Millions of Russians were ready to vote for the party, Rybakov, who has not received approval to stand as a candidate but attended the hearing on behalf of the party, told the court.
Rybakov described the proceedings against his party as "historic," saying that never before has a party been excluded from an election after having been granted approval to participate.
A representative for the electoral commission said in his closing statement that the foreign funding received by Yabloko made him reconsider the unanimous decision by the body to allow the party to participate in the vote.
Yabloko has been campaigning under the slogan "For Peace and Freedom," promising a "life without fear" in light of the political repression in Russia.
Rybakov ended his statement by stressing that the most important thing was for the killing to stop.
He accused Rodina of failing to present any evidence to support its allegations, accusing the party of putting forward fabrications and absurd ideas.
"The claimant is confusing the courtroom with a television talk show, where loud slogans, labels such as extremism and subjective associations take the place of the law," said Rybakov in response to the accusations.
Yabloko's long history shows that it is "an exclusively peaceful, civilized and lawful political organization," he added.
Rodina is considered a fringe party with no political clout that observers believe serves as a tool for the Kremlin.
Judge Kirillov has also been accused by the Russian opposition of serving the Kremlin's interests.
In another controversial trial, he banned Memorial, a human rights organization that was awarded the Nobel Peace Prize.
A Rodina representative criticized in court that Yabloko's election manifesto consisted of just 43 words and that its call for a ceasefire in the war against Ukraine was at odds with the war aims.
All other Russian parties support the war.
Observers have attributed the attack on Yabloko to a surge in support for the party seen since it was cleared to stand in the election – speculating that it might have become too great a risk for the Kremlin.
According to opinion polls, the party would have had a chance of clearing the 5% threshold and returning to the Duma for the first time in more than 20 years.
Yulia Navalnaya, the wife of late Russian dissident Alexei Navalny who died in a Siberian prison camp, said Monday's ruling showed that "the Kremlin is scared."
Other pro-Kremlin parties have also called for Yabloko's exclusion from the vote scheduled for September 18-20.
Several Duma deputies who support Russia's war against Ukraine have branded Yabloko members as traitors and agents of the West. Particular criticism has been directed at the fact that not a single war veteran appears on Yabloko's electoral list.
Most recently, Kremlin opponents living in exile abroad - who are persecuted in Russia as extremists and terrorists - called on voters to support the party.
This drew criticism within Yabloko itself, with members fearing it would provide additional "argumentative ammunition" for pro-Kremlin forces and jeopardize the party's electoral approval.
The nationwide parliamentary and local elections are scheduled for September 18 to 20. A total of eleven parties were approved to take part in the State Duma election. Currently, five political forces are represented in parliament.