California Code, Public Utilities Code - PUC § 1792

In case of the refusal of any witness to attend or testify or produce any papers required by a subpena issued by the commission or any commissioner, the commission or the commissioner may file, in the superior court in and for the county, or city and county, in which the proceeding is pending, a petition, setting forth that due notice has been given of the time and place of attendance of the witness, or the production of the papers, and that the witness has been summoned in the manner prescribed in this part and has failed and refused to attend or produce the papers required by the subpena, or has refused to answer questions propounded to him in the course of the proceeding.  The petition shall include a request for an order of the court, compelling the witness to attend and testify or produce the papers before the commission.