Newsom plans to announce on Wednesday plans to grant a reprieve to all of California's condemned prisoners on death row, two sources familiar with the situation said.
It was not immediately clear what form the reprieve may take.
NBC News was unable to reach the governor's office for comment Tuesday night.
Michele Hanisee, president of the Association of Deputy District Attorneys in Los Angeles, said in a statement Tuesday that voters have continually supported the use of the death penalty.
Hanisee also said voters in the state rejected propositions to end the practice in both 2006 and 2016.
"Governor Newsom, who supported the failed initiative to end the death penalty in 2006, is usurping the express will of California voters and substituting his personal preferences via this hasty and ill-considered moratorium on the death penalty," the statement said.
California's Supreme Court ruled in 1972 that capital punishment amounted to cruel and unusual punishment. State lawmakers re-enacted the death penalty statute in 1977 before voters reaffirmed capital punishment at the ballot box in 1978.
The state has executed 13 inmates since 1976, according to the Death Penalty Information Center. California has 740 inmates on death row, the non-profit organization reported.