Covered California will add a surcharge to "silver-level" policies next year unless the new administration can guarantee they'll pay Obamacare's cost-sharing subsidies.
Feeling the uncertainty, Anthem Blue Cross has withdrawn from 16 of the state's 19 pricing regions.
The pull out will affect almost 153,000 customers, or approximately 59 percent of its current enrollment rate.
The Los Angeles Times reports that only customers in Santa Clara County, parts of NorCal and the Central Valley will be able to purchase plans though Anthem.
Trump has used the funding of Obamacare's cost-sharing subsidies to help in his battle to repeal the health reform law.
He has threatened to stop sending insurers these payments, which would reduce deductibles and co-pays for low-income enrollees.
The uncertainty has caused insurers nationwide to hike rates or abandon the Obamacare exchanges for 2018.