Cal. Insurance Code § 1853.5

With respect to any matters pertaining to the making of rates or rating systems, the preparation or making of insurance policy or bond forms, underwriting rules, surveys, inspections and investigations, the furnishing of loss or expense statistics or other information and data, or carrying on of research, two or more admitted insurers having a common ownership or operating in this State under common management or control, are hereby authorized to act in concert between or among themselves the same as if they constituted a single insurer, and to the extent that such matters relate to co-surety bonds, two or more admitted insurers executing such bonds are hereby authorized to act in concert between or among themselves the same as if they constituted a single insurer.