California Code, Insurance Code - INS § 12957

The commissioner shall not withdraw approval of a previously approved policy, except upon those grounds as, in the commissioner's opinion, would authorize disapproval upon original submission thereof.  Any withdrawal of approval shall be in writing and shall specify the ground thereof.  If the insurer demands a hearing on a withdrawal, the hearing shall be granted and commenced within 30 days of the filing of a written demand with the commissioner.  Unless the hearing is commenced, the notice of withdrawal shall become ineffective upon the 31st day from and after the date of filing of the demand.

This section shall not apply to policies subject to the provisions of subdivision (f) of Section 10291.5, or to policies, contracts, or agreements that were approved under an alternative filing and approval procedure as provided for in subdivision (f) of Section 10506.4 or subdivision (c) of Section 10507.5.