California Code, Public Utilities Code - PUC § 8251

It is unlawful for any public service corporation, or agent, superintendent, or manager thereof, employing any special agent, detective, or person commonly known as a “spotter,” for the purpose of investigating, obtaining, and reporting to the employer information concerning its employees, to discipline or discharge any employee, where such act of discipline or the discharge is based upon a report by such special agent, detective, or spotter, which report involves a question of integrity, honesty, or a breach of rules of the employer, unless such employer, its agent, superintendent, or manager, gives notice and accords a hearing to the employee thus accused, when requested by the employee. At such hearing the employer shall state specific charges on which act of discipline or discharge is based, and the accused employee shall have the right to furnish testimony in his defense.