Peace groups outside the main gate of Beale Air Force Base on Wednesday protested the treatment of the private suspected of handing secret reports over to WikiLeaks.
They also called on military personnel at the base to resist war and the use of drones.
Protesters from Veterans for Peace, CodePink and other groups asked for "basic constitutional principles and human rights" be extended to Pfc. Bradley Manning.
Manning is suspected of downloading thousands of secret reports and diplomatic cables and handing them over to WikiLeaks.
The protesters encouraged members of the military at the base near Marysville to support Manning "for revealing the truth to the world community about the failed war of terror," said Toby Blome of CodePINK in a news release.
Manning is being held in solitary confinement at the Quantico Marine Base in Virginia on charges that could lead to a 52-year prison sentence.
Last month, protesters gathered at the base to protest the use of drones, an issue they renewed Wednesday.
The Associated Press has reported that the United States is increasingly relying on the missile strikes by drones flying over Pakistani territory to find and kill extremists that have free rein in the lawless areas along the border, where they plan attacks against U.S. and NATO troops in Afghanistan.
The United States launched more than 100 strikes this year, killing hundreds. Most have been in North Waziristan, where the Pakistani military has refused to stage its own ground offensive against the militant mini-state.