California Code, Labor Code - LAB § 1401

(a) An employer may not order a mass layoff, relocation, or termination at a covered establishment unless, 60 days before the order takes effect, the employer gives written notice of the order to the following:

(b) An employer required to give notice of any mass layoff, relocation, or termination under this chapter shall include in its notice the elements required by the federal Worker Adjustment and Retraining Notification Act (29 U.S.C. Sec. 2101 et seq.).

(c) Notwithstanding the requirements of subdivision (a), an employer is not required to provide notice if a mass layoff, relocation, or termination is necessitated by a physical calamity or act of war.