(1) The commission shall have the power to summon witnesses, to administer oaths and to require the production of records, books and documents for examination at any hearing or investigation conducted by it. Any oral or documentary evidence may be received, but the commission shall as a matter of policy provide for the exclusion of irrelevant, immaterial or unduly repetitious evidence, and no decision shall be rendered, sanction imposed or rule or order issued except on consideration of the whole record or such portions thereof as may be cited by any party and as supported by and in accordance with a preponderance of the reliable probative and substantial evidence. Every party shall have the right to present his case or defense by oral or documentary evidence, to submit rebuttal evidence, and to conduct such cross-examination as may be required for a full and true disclosure of facts. No person shall be excused from attending and testifying, or from producing books, papers and records before the commission or a court, or from obedience to the subpoena of the commission or a court, on the ground or for the reason that the testimony or evidence, documentary or otherwise, required of him may tend to incriminate him or subject him to a penalty or forfeiture; Provided, that nothing in this subsection shall be construed as requiring any person to produce any books, papers or records or to testify in response to any inquiry not pertinent to some question lawfully before such commission or court for determination. No natural person shall be subjected to criminal prosecution or to any penalty or forfeiture for or on account of any transaction, matter or thing concerning which, in spite of his objection, he may be required to testify or produce evidence, documentary or otherwise, before the commission or court, or in obedience to its subpoena; Provided, that no person testifying shall be exempted from prosecution and punishment for perjury committed in so testifying.
(2) In case of failure or refusal on the part of any person to comply with the subpoena issued by the commission, or in case of the refusal of any witness to testify as to any matter regarding which he may be lawfully interrogated, any district court in the state, upon the application of the commission, may in term time or vacation issue an attachment for such person and compel him to comply with such subpoena, and to attend before the commission and produce such records, books and documents for examination, and to give his testimony. Such court shall have the power to punish for contempt as in the case of disobedience to a like subpoena issued by the court, or for refusal to testify therein.