MOSCOW — A Moscow court on Monday ordered the closing of a foundation supporting the activities of Aleksei A. Navalny, the country’s leading opposition politician, moving quickly in a case filed only this month by the Justice Ministry.

The court order came before a series of rallies in more than 90 Russian cities and towns, scheduled for Sunday and organized by Mr. Navalny and his supporters.

The foundation, the Fifth Season of the Year, has been used by Mr. Navalny to collect donations that finance campaign materials, salaries and offices in 84 regions across Russia, among other weapons in his drive against corruption and the workings of the Kremlin under President Vladimir V. Putin. More than 145,000 Russians have donated $4.9 million to the foundation over the past 13 months, Mr. Navalny says.

At the end of December, Russian election officials barred Mr. Navalny from running in the presidential election scheduled for March, citing his suspended sentence in a fraud case that he and his supporters have denounced as politically motivated.