California Code, Labor Code - LAB § 6601

If within 15 working days from receipt of the citation or notice of civil penalty issued by the division, the employer fails to notify the appeals board that he intends to contest the citation or notice ofproposed penalty, and no notice contesting the abatement period is filed by any employee or representative of the employee within such time, the citation or notice of proposed penalty shall be deemed a final order of the appeals board and not subject to review by any court or agency.  The 15-day period may be extended by the appeals board for good cause.