(A) Any person may petition for leave to intervene in an appeal before the commission, which appeal has been initiated by another party. A petition for leave to intervene must be filed no later than seven days prior to the scheduled evidentiary hearing in the matter, unless waived by the commission for extraordinary cause. A petitioner for intervention shall have the burden of showing an interest which is or may be affected by the outcome of a proceeding before the commission.
(1) In determining whether intervention is appropriate, the commission shall determine if the person petitioning for intervention was adversely affected under section 1509.36 of the Revised Code by the order that is the subject of the appeal before the commission.
(2) In addition to the requirement established in paragraph (B)(1) of this rule, the commission may consider the following in determining whether intervention is appropriate:
(a) The nature of the issues;
(b) The adequacy of representation of the petitioner's interest which is provided by the existing parties to the proceeding;
(c) Delay or prejudice to the existing parties to the proceeding; and
(d) The ability of the petitioner to present relevant evidence and argument.
(C) The commission shall determine whether a person petitioning to become an intervenor may participate in such proceeding using the factors established in paragraph (B) of this rule. The extent and the terms of the participation shall be in the discretion of the commission and shall be set forth when the commission rules upon the petition for intervention.
(D) The commission may allow the filing of briefs and permit oral argument at hearing by an amicus curiae. A person wishing to participate in an appeal as an amicus curiae shall move the commission for permission to so participate. Amicus curiae participation is discretionary and will be permitted only upon the terms and conditions imposed by the commission.