California is about to begin desegregating its prison cells, and that worries inmates and prison officials alike.

For years, the state’s prison system used race as a criterion when initially designating cellmates. Prisons paired incoming white inmates with white, black with black, Hispanic with Hispanic. The unwritten policy aimed to avoid interracial tensions among gang members. But in 2005, after a 10-year legal battle, the U.S. Supreme Court ruled that California’s prisons can’t use race to determine cell assignments. So, in coming weeks, California plans to start desegregating cells in the largest state-prison system in the U.S. Among the first to be integrated will be Mule Creek State Prison in Ione and Sierra Conservation Center in Jamestown. State officials say they expect California’s 28 other state prisons to follow suit by 2010. Some inmates expect an increase in violence to follow. “There’s going to be a lot of killing,” says Randy Torrez, a former Mexican Mafia gang member, in an interview at the Mule Creek prison, where he is an inmate. “These people have been fighting for the majority of their lives, and it just gets worse [in prison]. It’s not going to work.” California is one of only a few states to acknowledge the use of such systematic segregation in cells. Texas and Oklahoma once had similar practices in place but have dismantled them. Some other individual prisons in the U.S. probably use race as a criterion in choosing cellmates, says Chad Trulson, a professor of criminal justice at the University of North Texas, but there are no reliable data. Prof. Trulson, who has studied the effects of Texas’s desegregation program, says state facilities take varying approaches to handling gang activity and violence and few publicly acknowledge their approaches.