Cal. Code Regs. tit. 10 § 2237.3
The reduction in benefits provision in each group disability income policy issued, issued for delivery or renewed in this State after the effective date of this regulation shall provide in substance that in the case of duplicating insurance the liability of the insurer under its group disability income policy shall not be less than its pro rata share of the maximum net benefit, which pro rata share shall be determined by dividing the net benefit payable by the insurer under its group disability income policy by the total of all net benefits under all group disability income policies under which the insured is entitled to receive benefits and multiplying that result by the maximum net benefit.
No reduction of benefits provision in a group disability income policy not containing the standards described in this section or standards not less favorable to the insured shall be approved by the Commissioner. The reduction of benefits provision in each group disability income policy heretofore issued in this State, which is renewed after the effective date of this regulation, shall be amended to contain the standards described in this section or standards not less favorable to the insured.
Cal. Code Regs. Tit. 10, § 2237.3