Two guards and a chaplain have been released from a hospital after being hurt in an attack at the Menard Correctional Center.
Union officials say the incident involved up to 15 inmates, and the attack led to a lockdown of the facility.
Last Thursday, a Menard inmate died in what one official calls suspicious circumstances.
Union officials say the violence is a result of Illinois Gov. Pat Quinn's decision to close several prisons around the state to save money.
Tuesday's assaults happened as about 200 union members marched outside the prison. They were protesting over what they say are growing threats to their safety.
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