"We condemn the solitary confinement that Chelsea Manning has been subjected to during her incarceration at William G. Truesdale adult detention center," a committee of supporters said in a statement.
According to supporters group, Chelsea Manning has been kept in a cell for 22 hours a day, which could affect the former army specialist's mental health.
"Chelsea can't be out of her cell while any other prisoners are out, so she cannot talk to other people, or visit the law library, and has no access to books or reading material. She has not been outside for 16 days," they added.
Manning, formerly known as Bradley Manning, was released from a US prison in May 2017 after serving seven years of a 35-year prison sentence for handing over internal documents to WikiLeaks. The sentence was commuted by then-US President Barack Obama in 2017 as one of his last official acts.