Cal. HSC § 1367.8

No plan issuing, providing, or administering any individual or group health care service plan entered into, amended, or issued on or after January 1, 1981, shall refuse to cover, or refuse to continue to cover, or limit the amount, extent or kind of coverage available to an individual, or charge a different rate for the same coverage solely because of a physical or mental impairment, except where the refusal, limitation or rate differential is based on sound actuarial principles applied to actual experience, or, if insufficient actual experience is available, then to sound underwriting practices.

This section shall not apply to a health maintenance organization qualified pursuant to Title XIII of the federal Public Health Service Act if such organization gives public notice 30 days in advance, in a newspaper of general circulation published in the area served by the health maintenance organization, of its open enrollment period required by such act.