California Code, Health and Safety Code - HSC § 1367.23

(a) On and after January 1, 1994, every group health care service plan contract, which is issued, amended, or renewed, shall include a provision requiring the health care service plan to notify the group contractholders in writing of the cancellation of the plan contract and shall include in their contract with group contractholders a provision requiring the group contractholder to mail promptly to each subscriber a legible, true copy of any notice of cancellation of the plan contract which may be received from the plan and to provide promptly to the plan proof of that mailing and the date thereof.

(b) The notice of cancellation from the group contractholder to the subscriber required by subdivision (a) shall include information regarding the conversion rights of persons covered under the plan contract upon termination of the plan contract. This information shall be in clear and easily understandable language.