If a petition to intervene shows direct and substantial interest in any part of the subject matter of a proceeding and does not unduly broaden the issues, the Commission or the presiding officer will grant intervention, subject to reasonable conditions. If it later appears that an intervenor has no direct or substantial interest in the proceeding, or that the intervention is not in the public interest, the Commission may dismiss the intervenor from the proceeding.
Idaho Admin. Code r. 31.01.01.074