A panel of federal judges Wednesday refused to delay its order that California release nearly 10,000 additional prison inmates by the end of the year.
The decision rejecting a request by Gov. Jerry Brown pushed the long-running court battle back to the U.S. Supreme Court to consider whether poor medical and mental health care violate the constitutional rights of inmates.
The Brown administration said it would seek a stay from Justice Anthony Kennedy if the delay was denied. Kennedy oversees appeals from western states.
If Kennedy declines to intervene, the state has said it will begin freeing inmates to comply with the lower court order.
"After this long history of defendants' noncompliance, this court cannot in good conscience grant a stay that would allow defendants to both not satisfy the population reduction order and re-litigate the Supreme Court's emphatic decision in the very case before us," the court said in its 24-page ruling.
Brown's office referred a request for comment to the state corrections department.
"We look forward to making our case to the Supreme Court justices that no further reduction in the prison population is needed," Deborah Hoffman, a spokeswoman for the Department of Corrections and Rehabilitation, said in an emailed statement.
The lower court last month instructed the Democratic governor to immediately begin taking steps that include expanding good-time credits leading to early release to reduce crowding and improve inmate care.
The three judges again rejected Brown's argument that doing so would threaten public safety.
Other states have used similar measures to reduce their inmate populations, the judges said, and the early release credits were endorsed by experts including Jeffrey Beard before he became California's corrections secretary.
"We're very close to actually having the state grapple with the important public policy questions and stop the legal games. They get one last stay motion and then we can finally get down to business," said Ernie Galvan, one of the attorneys who sued on behalf of mentally ill inmates.
The judges have repeatedly accused Brown of deliberately attempting to delay and circumvent their orders that the state reduce the population in its 33 adult prisons to about 110,000 inmates by year's end.
The orders enforce a 2009 ruling by the panel that reducing prison crowding to that level is necessary to improve the care of sick and mentally ill inmates.
The Supreme Court backed the lower court's ruling in a 5-4 decision in May 2011. Kennedy, an appointee of Republican President Ronald Reagan, sided with the court's four Democrat-appointed justices to cast the deciding vote against the state.
But Brown has argued that the state already has reduced what once was the nation's largest state prison population by more than 46,000 inmates since 2006, with more than half the decrease due to a 2-year-old state law that is sentencing lower-level criminals to county jails instead of state prisons.
Releasing the final 10,000 inmates now will overwhelm law enforcement and cause irreparable harm to public safety because inmates, once released, cannot be returned to prison if the nation's high court eventually rules in the state's favor, the administration argues.
Attorneys representing inmates countered in their own court filing that the state has had two years to comply, using measures that already have been approved by the courts.
Further delay now "will prolong ongoing irreparable harm - including illness and death" for inmates, they argue.