Oil spilling into federal waters off California's coast has prompted fresh calls for an end to offshore oil drilling in state and federal waters — but that's easier said than done.

Neither the longstanding ban on new drilling leases in state water nor an effort in Congress to ban new leases in federal waters stop existing drilling.

California Gov. Gavin Newsom said Tuesday that it's easier to ban new drilling than to wind down what already exists.

"Banning new drilling is not complicated," he said, according to The Associated Press. "The deeper question is how do you transition and still protect the workforce?"

He added that the most recent spill has added to the urgency to curb oil production.

"It's time, once and for all, to disabuse ourselves that this has to be part of our future. This is part of our past," he said alongside other elected officials.

California remains the nation's seventh-largest oil-producing state, and winding down the state's oil production has proved politically difficult. The industry employs more than 150,000 people, and the state makes money from oil and gas leases.

Efforts to plug and decommission several state oil platforms are underway, but the process is costly and time-consuming. It's expected to cost more than $800 million to decommission wells in the Wilmington Oil Fields off the coast of Long Beach. The state has just $300 million set aside.

"It boils down to finances and priorities," Democratic state Assemblyman Patrick O'Donnell said. "I would hope that as we move forward, we look at those wells ceasing to operate as soon as possible."