California on Friday banned private prisons and immigrant detention centers under a bill signed by the liberal state's governor.
The measure stipulates that beginning next year, the state's Department of Corrections and Rehabilitation is prohibited from entering into or renewing a contract with a private, for-profit prison to incarcerate people.
The bill also calls for such facilities to be phased out by 2028.
"During my inaugural address, I vowed to end private prisons, because they contribute to over-incarceration, including those that incarcerate California inmates and those that detain immigrants and asylum seekers," Newsom, who has repeatedly sparred with the Trump administration over immigration, said after signing the bill.
"These for-profit prisons do not reflect our values," he added
California lawmaker Rob Bonta, who authored the bill, described the signing as "a truly historic moment for California."
"By ending the use of for-profit, private prisons and detention facilities, we are sending a powerful message that we vehemently oppose the practice of profiteering off the backs of Californians in custody, that we will stand up for the health, safety and welfare of our people, and that we are committed to humane treatment for all," he told a news conference.
Rights advocates also hailed the measure, pointing to what has been described as inhumane conditions at many of the private facilities where several inmates have died in recent years.
Mario, a 31-year-old Mexican immigrant who spoke at the news conference, said he had spent six months at one of these for-profit detention centers and had "experienced first-hand the injustice, the lack of medical care, the lack of nutritious food, the lack of everything."
"This is completely unacceptable," he said. "People's lives are at stake and people's lives have been lost because of this."
There are currently some 115,000 inmates being held at California prisons, and approximately 1,700 of them are housed in private facilities.
The state was previously notorious for its prison overcrowding but federal judges in 2009 imposed a cap, leading to privately outsourced incarceration.
There are currently four dedicated immigration detention facilities in California with an inmate population of about 3,700, officials say.
Bryan Cox, acting press secretary for US Immigration and Customs Enforcement (ICE) told local media that the new bill signed Friday would not deter immigration enforcement.
"ICE would simply have to transfer individuals a greater distance from their arrest location," he told local media.
"The greatest impact would be felt by California residents, who would be forced to travel longer distances to visit friends and family in detention."