Cal. LAB § 3762

(a) Except as provided in subdivisions (b) and (c), the insurer shall discuss all elements of the claim file that affect the employer’s premium with the employer, and shall supply copies of the documents that affect the premium at the employer’s expense during reasonable business hours.

(b) The right provided by this section shall not extend to any document that the insurer is prohibited from disclosing to the employer under the attorney-client privilege, any other applicable privilege, or statutory prohibition upon disclosure, or under Section 1877.4 of the Insurance Code.

(c) An insurer, third-party administrator retained by a self-insured employer pursuant to Section 3702.1 to administer the employer’s workers’ compensation claims, and those employees and agents specified by a self-insured employer to administer the employer’s workers’ compensation claims, are prohibited from disclosing or causing to be disclosed to an employer, any medical information, as defined in Section 56.05 of the Civil Code, about an employee who has filed a workers’ compensation claim, except as follows:

(1) Medical information limited to the diagnosis of the mental or physical condition for which workers’ compensation is claimed and the treatment provided for this condition.

(2) Medical information regarding the injury for which workers’ compensation is claimed that is necessary for the employer to have in order for the employer to modify the employee’s work duties.