California Code, Public Utilities Code - PUC § 1795

No person shall be excused from testifying or from producing any book, waybill, document, paper, or account in any investigation or inquiry by or hearing before the commission or any commissioner, when ordered to do so, upon the ground that the testimony or evidence, book, waybill, document, paper, or account required of him may tend to incriminate him or subject him to penalty or forfeiture, but no person shall be prosecuted, punished, or subjected to any penalty or forfeiture for or on account of any act, transaction, matter or thing concerning which, under oath, he has testified or produced documentary evidence, but no person so testifying shall be exempt from prosecution or punishment for any perjury committed by him in his testimony. Nothing herein contained shall be construed as in any manner giving to any public utility immunity of any kind.