At any investigation by or proceeding before the public utilities commission the public utility or the person concerned, or other respondent or party and any complainant or permitted intervenor shall have the right to be present and represented by counsel, to present any evidence desired, and to cross-examine any witness who may be called.
HRS § 269-13
Intervention as party is a matter within sound discretion of the commission. 56 H. 260, 535 P.2d 1102.