Cal. Ins. Code § 796.04
A health insurer that provides coverage for hospital, medical, or surgical expenses that authorizes a specific type of treatment for services covered under a policyholder's contract or plan by a provider shall not rescind or modify this authorization after the provider renders the health care service in good faith and pursuant to the authorization for any reason, including, but not limited to, the insurer's subsequent rescission, cancellation, or modification of the insured's or policyholder's contract or the insurer's subsequent determination that it did not make an accurate determination of the insured's eligibility. This section shall not be construed to expand or alter the benefits available or the terms and conditions of the contract as may be agreed upon between a policyholder, certificate holder, or trust, and the insurer. The Legislature finds and declares that by adopting the amendments made to this section by Assembly Bill 1324 of the 2007-08 Regular Session it does not intend to instruct a court as to whether or not the amendments are existing law.
Ca. Ins. Code § 796.04