California Code, Labor Code - LAB § 4610.3

(a) Regardless of whether an employer has established a medical provider network pursuant to Section 4616 or entered into a contract with a health care organization pursuant to Section 4600.5, an employer that authorizes medical treatment shall not rescind or modify that authorization after the medical treatment has been provided based on that authorization for any reason, including, but not limited to, the employer's subsequent determination that the physician who treated the employee was not eligible to treat that injured employee. If the authorized medical treatment consists of a series of treatments or services, the employer may rescind or modify the authorization only for the treatments or services that have not already been provided.

(b) This section shall not be construed to expand or alter the benefits available under, or the terms and conditions of, any contract, including, but not limited to, existing medical provider network and health care organization contracts.

(c) This section shall not be construed to impact the ability of the employer to transfer treatment of an injured employee into a medical provider network or health care organization. This subdivision is declaratory of existing law.

(d) This section shall not be construed to establish that a provider of authorized medical treatment is the physician primarily responsible for managing the injured employee's care for purposes of rendering opinions on all medical issues necessary to determine eligibility for compensation.