Cal. Pub. Util. Code § 2101
The commission shall see that the provisions of the Constitution and statutes of this State affecting public utilities, the enforcement of which is not specifically vested in some other officer or tribunal, are enforced and obeyed, and that violations thereof are promptly prosecuted and penalties due the State therefor recovered and collected, and to this end it may sue in the name of the people of the State of California. Upon the request of the commission, the Attorney General or the district attorney of the proper county or city and county shall aid in any investigation, hearing, or trial had under the provisions of this part, and shall institute and prosecute actions or proceedings for the enforcement of the provisions of the Constitution and statutes of this State affecting public utilities and for the punishment of all violations thereof.
Ca. Pub. Util. Code § 2101