Cal. LAB § 554

(a) Sections 551 and 552 do not apply to cases of emergency or to work performed in the protection of life or property from loss or destruction, or to any common carrier engaged in or connected with the movement of trains. Nothing in this chapter shall be construed to prevent an accumulation of days of rest when the nature of the employment reasonably requires that the employee work seven or more consecutive days, if in each calendar month the employee receives days of rest equivalent to one day’s rest in seven. The requirement respecting the equivalent of one day’s rest in seven shall apply, notwithstanding the other provisions of this chapter relating to collective bargaining agreements, where the employer and a labor organization representing employees of the employer have entered into a valid collective bargaining agreement respecting the hours of work of the employees, unless the agreement expressly provides otherwise.

(b) In addition to the exceptions specified in subdivision (a), the Chief of the Division of Labor Standards Enforcement may, when in his or her judgment hardship will result, exempt any employer or employees from the provisions of Sections 551 and 552.