Cal. Lab. Code § 5307.11
A health care provider or health facility licensed pursuant to Section 1250 of the Health and Safety Code, and a contracting agent, employer, or carrier may contract for reimbursement rates different from those in the fee schedule adopted and revised pursuant to Section 5307.1. When a health care provider or health facility licensed pursuant to Section 1250 of the Health and Safety Code, and a contracting agent, employer, or carrier contract for reimbursement rates different from those in the fee schedule, the medical fee schedule for that health care provider or health facility licensed pursuant to Section 1250 of the Health and Safety Code shall not apply to the contracted reimbursement rates. Except as provided in subdivision (b) of Section 5307.1, the official medical fee schedule shall establish maximum reimbursement rates for all medical services for injuries subject to this division provided by a health care provider or health care facility licensed pursuant to Section 1250 of the Health and Safety Code other than those specified in contracts subject to this section.
Ca. Lab. Code § 5307.11