The Moscow City Court also was to set a date for the trial of Udaltsov, who heads the Left Front organization, and his associate Leonid Razvozzhayev, who is already in custody, Interfax reported.
The two activists are accused of organizing clashes between anti-Kremlin protesters and the police in May 2012 "with the goal of encroaching on the foundation of stability and security in society and destabilizing the social and political situation in the Russian Federation," according to court documents prepared by investigators.
The charge made them ineligible for a presidential amnesty passed last week that exonerated four other people arrested in connection to the protest.
Investigators also accuse Udaltsov and Razvozzhayev of "planning further actions aimed at organizing mass riots" across Russia. The defendants and their alleged accomplices are accused of running "training camps" and "recruiting participants for the planned riots," the Prosecutor General's Office said in a statement carried by Interfax.
Udaltsov has been under house arrest since the start of this year.
Razvozzhayev, a Left Front member and an aide to State Duma Deputy Ilya Ponomaryov, has been held in pre-trial detention since his arrest in Kiev in October 2012. Investigators accuse him of illegally crossing the Russian border on his brother's passport. Razvozzhayev has said Russian security services kidnapped him in Kiev and tortured him into confessing.
Another Left Front member, Konstantin Lebedev, has pleaded guilty to the same charge of organizing riots and received a reduced prison sentence of 2.5 years under a plea bargaining deal.
Udaltsov and Razvozzhayev face up to 10 years in prison if convicted.
