A panel of federal judges on Thursday issued a 71-page ruling that rejected Gov. Jerry Brown's attempt to overturn the court's restrictions on crowding in prisons, the Los Angeles Times reported.
Brown and other officials "will not be allowed to continue to violate the requirements of the Constitution of the United States," the judges wrote.
In January, Brown said his state's prison crisis had ended and launched a campaign to regain control of the prisons' healthcare system, which has been overseen by the court since 2006.
However, in its ruling Thursday, the court said Brown had provided "no convincing evidence" that overcrowding within the prison systems had been resolved.
"At no point over the past several months have defendants indicated any willingness to comply, or made any attempt to comply, with the orders of this court," they said. "In fact, they have blatantly defied them."
The judges gave the state 21 days to come up with a plan to meet the prison population target by the end of the year, or Brown and other state officials will be held in contempt of court.
California's prisons currently hold 119,542 inmates -- 149.5 percent of the number they were designed to hold, said a report released this week by California Department of Corrections and Rehabilitation.
Deborah Hoffman, a spokeswoman for the corrections department, criticized the court's ruling, saying. "The truth of the matter is that California has invested more than a billion dollars to transform its prison health care system into one of the best in the country. Our prisons now provide timely and effective health care to inmates that far exceeds what the Constitution requires."