KNOXVILLE — A nonprofit group that advocates for prisoners' rights says Knox County is censoring its mail to inmates, and it's seeking a court order to stop the practice.

Prison Legal News filed its lawsuit Tuesday in federal court in Knoxville. The nonprofit claims the Knox County Jail has censored at least 147 items it has sent to inmates since November 2014. Items that never made it to their intended recipients include the nonprofit's monthly journal, also called Prison Legal News, as well as books, brochures and fundraising materials.

Jail policy says all personal mail to inmates must be on standard-size postcards with pre-printed stamps, according to the lawsuit.

The suit claims the jail policy is arbitrary and violates the plaintiff's free-speech right to communicate with inmates.

"As part of its organizational mission, PLN engages in core protected speech on matters of public concern, such as prison operations and conditions, legal updates on prison litigation, prisoner health and safety, and prisoners' rights," the lawsuit states.

A spokeswoman for the Knox County Sheriff's Office says they don't comment on pending litigation. The suit names Sheriff Jimmy "J.J." Jones, Assistant Chief Deputy Rodney Bivens and Knox County as defendants.

The suit says Prison Legal News regularly sends its publications to prisoners in more than 2,600 correctional facilities across all 50 states, including prisoners in death row units and "supermax" prisons.

"It cannot reasonably be argued that there is any 'valid, rational connection' between the Jail's policies and practices and any legitimate governmental interest that could be put forward to justify them," the suit states.

Prison Legal News is asking the court for a temporary order to stop the censorship while the case makes its way through the courts. Eventually, it seeks a ruling that the policy is unconstitutional.