Chelsea Manning, the American soldier serving a 35-year prison sentence for a massive leak of classified US documents, could be placed in solitary confinement, her supporters said.
Manning on Tuesday (local time) will be the subject of disciplinary proceedings for "disorderly conduct" during a prison meal, and "disrespect" towards a prison guard during the incident, they said.
She is also reported to have been in possession of contraband books, magazines and expired toothpaste, according to the website chelseamanning.org, which published the charges.
It added that Manning, who underwent hormone treatment to become a woman, was in possession of the Vanity Fair magazine featuring Caitlyn Jenner, the former US Olympian who underwent a sex change.
The prison administration said that "the maximum charges for these offences is indefinite solitary confinement", according to the Manning website.
The US Army confirmed that Manning was the subject of disciplinary proceedings, without specifying the charges or potential penalties.
Manning, who was formerly a male enlistee known as Bradley Manning, is serving out her sentence at Fort Leavenworth prison in Kansas.
After months of legal wrangling, the US Army approved hormone therapy for Manning's gender "reassignment", an unprecedented step for the military.
The former army intelligence analyst was convicted in August 2013 of espionage and other offences after admitting to handing more than 700,000 classified documents, including military intelligence reports and State Department cables, to the anti-secrecy website WikiLeaks.
US officials describe Manning's document dump as the biggest leak of classified files in American history.
Manning is a regular contributor to the press through her social network, and writes occasional commentaries for The Guardian newspaper's American edition, offering her take on US foreign policy.
She began posting on Twitter in April with help from supporters.