The former U.S. Army soldier, already imprisoned for providing classified documents to Wikileaks, was found guilty Tuesday on four charges, the inmate tweeted.
"I am receiving 21 days of restrictions on recreation -- no gym, library or outdoors," Manning tweeted.
Those four charges include medicine misuse, prohibited property, disorderly conduct and disrespect.
The medicine charge came after officials discovered an expired tube of toothpaste in her cell, according to a statement on ChelseaManning.org
The contraband came in the form of books and magazines -- such as a copy of Vanity Fair magazine featuring Caitlyn Jenner
and a copy of Cosmopolitan magazine featuring an interview with Manning. But according to ChelseaManning.org, she received the reading material legally through the prison's open mail system.
The disorderly conduct and disrespect charges both stem from an incident during dinner on July 2. Officials accused Manning of "sweeping food onto the floor" and conducting herself "in a contemptuous manner by being disrespectful to the cadre present." ]
A U.S. Military spokesman declined to comment, citing that the proceedings were "protected by the Privacy Act of 1974."
The statement on Manning's website offers her explanation of what happened.
"The catalyst for this attack on Chelsea seems to have been an incident in the mess hall where she may have pushed, brushed, or accidentally knocked, a small amount of food off of her table," the statement said. "She then asked to speak to her lawyer when confronted by a guard. The absurd charges were tacked on later."
According to the statement, the four charges could have been punishable by "indefinite solitary confinement."
"These absurd charges against Chelsea, and the outrageous threat of indefinite solitary confinement, are clearly an attempt to silence Chelsea's important voice and cut her off from the outside world," the statement said.
Manning is serving a 35-year prison sentence at Fort Leavenworth, an Army prison in eastern Kansas, for leaking a trove of classified documents to Wikileaks. She was convicted of violating the Espionage Act.
Manning, who was born male and was formerly known as Bradley Manning, said two years ago
that she is female. She eventually filed a lawsuit in federal court claiming she "has been denied access to medically necessary treatment" for her gender disorder.
Manning regularly publishes op-eds in The Guardian about transgender rights, the prison system and government transparency, according to the statement. She recently won the ability to begin hormone therapy after threatening to sue the military.