(a) After service of the petition on the commission and within the time permitted for filing an answer or within additional time allowed by the court, the commission shall send to the reviewing court the original or a certified copy of the entire record of the proceeding under review.
(b) The record shall be filed with the clerk of the court. The record may be shortened by stipulation of all parties to the review proceedings. The court may assess additional costs against a party who unreasonably refuses to stipulate to limit the record, unless the party pays all costs of record preparation.