Mikhail Khodorkovsky, once Russia's richest man, appears to have teamed up with firebrand opposition activist Alexei Navalny to organize a massive protest in central Moscow on March 1.
Under Russian law, city authorities must approve of such events in advance. Navalny and the other organizers mailed a letter to Moscow Mayor Sergei Sobyanin to warn City Hall of their intent to request permission. In a photograph of the letter posted to Navalny's website Monday, Khodorkovsky's signature was seen among those of the other organizers.
Khodorkovsky, a former oil tycoon who served a decade in Russian prison on charges he maintains were politically motivated, is not known to have re-entered Russia since leaving for Europe shortly after his 2013 release from prison.
However, last year he said he would be ready to serve as Russia's next president given the opportunity.
Navalny's website said Friday that the rally would comprise about 100,000 people, with a march down Moscow's central thoroughfare, Tverskaya Ulitsa.
The website said the rally would protest the current political "crisis," demanding the termination of the Western food import ban, the "propagandist hysteria in the media" and "all aggressive actions regarding Ukraine."
It would also call for the opposition to be allowed at least "one hour of airtime per week" on one of Russia's main state television channels. The letter also bore the signatures of opposition leaders Boris Nemtsov and Mikhail Kasyanov.
Navalny said Sunday that his Party of Progress intends to run in Russia's 2016 parliamentary elections. He said there was a "very high" chance that the government would block the party, and called for protests and rallies if that occurs, the Noviye Izvestia newspaper reported.