Idaho Admin. Code r. 31.01.01.073
Unless otherwise provided by Commission notice or order, petitions to intervene must be filed at least fourteen (14) days before (1) the deadline for filing initial comments, if the case is being processed by modified procedure under Rules 201 -204; or (2) the earlier of the dates set for the technical hearing or prehearing conference in cases in which a technical hearing is scheduled to occur. Petitions not timely filed must state a substantial reason for delay. The Commission may deny or conditionally grant untimely petitions for failure to state good cause for untimely filing, to prevent disruption, prejudice to existing parties or unduly broadening the issues, or for other reasons. If the Commission grants an untimely petition, then the petitioner is bound by the prior orders and notices in the proceeding.
Idaho Admin. Code r. 31.01.01.073