Cal. Lab. Code § 604

No person who by the use of the telegraph or telephone, dispatches, reports, transmits, receives or delivers orders pertaining to or affecting train movements shall be required or permitted to be on duty for a longer period than nine hours in any twenty-four hours, in towers, offices, places and stations continuously operated night and day, nor for a longer period than thirteen hours in towers, offices, places and stations operated only during the daytime. In case of emergency, however, the persons referred to in this section may be permitted to be on duty for four additional hours in a twenty-four hour period. Such additional duty shall not be required or permitted on more than three days in any week.