(Reuters) - California Governor Gavin Newsom proposed a plan on Thursday requiring oil refiners to maintain minimum reserves of gasoline in an effort to prevent price spikes.

The California Energy Commission said that on 63 days last year California refiners maintained less than 15 days of supply of gasoline, a situation that it said spiked prices and cost drivers $650 million.

"Price spikes at the pump are profit spikes for Big Oil. Refiners should be required to plan ahead and backfill supplies to keep prices stable, instead of playing games to earn even more profits," Newsom, a Democrat, said in a release.

It was unclear when the plan could take effect and Newsom's office did not immediately respond to a request for comment.

Under the plan, which industry has criticized as attacking producers, California's oil refiners would be required to demonstrate resupply plans that are adequate to address losses in production when their plants are undergoing maintenance work.

California found that in 2023 gasoline prices spiked largely due to refineries going offline without adequately planning to backfill supplies.

The plan comes three months after the U.S. Department of Energy sold its 1 million barrel Northeast gasoline reserve, which Washington created after 2014's Superstorm Sandy left motorists scrambling for fuel supplies. The U.S. Congress mandated the sale after the reserve was criticized as expensive to maintain and for not increasing energy security.

California, the most populous U.S. state, is home to some of the country's highest average gasoline prices and has had a fraught relationship with oil companies. The state has ambitious targets for electric car adoption and is the only one with a waiver from the federal environmental regulator to set its own vehicle emissions regulations.

This month, U.S. oil company Chevron said it was moving its headquarters to Houston from San Ramon, California.

Catherine Reheis-Boyd, president and CEO of the Western States Petroleum Association said Newsom's plan was "nothing more than a political attack on consumers and our industry." 

"To impose new operational mandates on energy producers based on such falsehoods is regulatory malpractice, and ignores the logistical challenges and costs associated with such a plan," she said.