California Code, Labor Code - LAB § 4625

(a) Effective for services provided on or after January 1, 2017, all bills for medical-legal evaluation or medical-legal expense shall be submitted to the employer within 12 months of the date of service in the manner prescribed by the administrative director.  The administrative director shall adopt rules to define circumstances that constitute good cause for an exception to the 12-month period.  Bills for medical-legal charges are barred unless timely submitted.

(b) Notwithstanding subdivision (d) of Section 4628, all charges for medical-legal expenses for which the employer is liable that are not in excess of those set forth in the official medical-legal fee schedule adopted pursuant to Section 5307.6 shall be paid promptly pursuant to Section 4622.

(c) If the employer contests the reasonableness of the charges it has paid, the employer may file a petition with the appeals board to obtain reimbursement of the charges from the physician that are considered to be unreasonable.