California Governor Jerry Brown is asking the Supreme Court to intervene in a battle over the state's prison population.
A federal court has ruled the state's prison system is over-crowded, and it's ordered thousands of prisoners to be released by the end of the year.
Over the years, California has sent far more criminals to state prisons than it has room for.
California's prisons are built to accommodate 80,000 prisoners, but there are almost 120,000.