Cal. Insurance Code § 922.31

(a) A ceding insurer shall take steps to manage its reinsurance recoverables proportionate to its own book of business. A domestic ceding insurer shall notify the commissioner within 30 days after reinsurance recoverables from any single assuming insurer, or group of affiliated assuming insurers, exceeds 50 percent of the domestic ceding insurer’s last reported surplus to policyholders, or after it is determined that reinsurance recoverables from any single assuming insurer, or group of affiliated assuming insurers, is likely to exceed this limit. The notification shall demonstrate that the exposure is safely managed by the domestic ceding insurer. (b) A ceding insurer shall take steps to diversify its reinsurance program. A domestic ceding insurer shall notify the commissioner within 30 days after ceding to any single assuming insurer, or group of affiliated assuming insurers, more than 20 percent of the ceding insurer’s gross written premium in the prior calendar year, or after it has determined that the reinsurance ceded to any single assuming insurer, or group of affiliated assuming insurers, is likely to exceed this limit. The notification shall demonstrate that the exposure is safely managed by the domestic ceding insurer.