Cal. Gov. Code § 3255

A firefighter shall not have any comment adverse to his or her interest entered in his or her personnel file, or any other file used for any personnel purposes by his or her employer, without the firefighter having first read and signed the instrument containing the adverse comment indicating he or she is aware of the comment. However, the entry may be made if after reading the instrument the firefighter refuses to sign it. That fact shall be noted on that document, and signed or initialed by the firefighter.