Upon timely motion and at the discretion of the commission or the hearings officer, any person may be permitted to intervene and be admitted as a party in a proceeding before the commission or hearings officer if that person has a substantial interest in the outcome of the proceeding which is not protected by the interests of any of the parties, or the intervention shall be conducive to effectuating the ends of justice and to achieving the goals and purposes of the commission; provided that no intervention shall be permitted if the intervention shall unduly delay the proceeding or harass, hinder, or prejudice the rights of any party to the proceeding.
Haw. Code R. § 3-161-7