Oregon Revised Statutes Utility Regulation § 756.525

(1) The Public Utility Commission may permit any person to become a party who might, on the institution of the proceeding, have been such a party, if application therefor is made before the final taking of evidence in the proceeding.

(2) At any time before the final taking of evidence in a proceeding, any person may apply to the commission for permission to appear and participate in the proceeding. The commission shall determine the interest of the applicant in the proceeding and shall grant the application, subject to appropriate conditions, if the commission determines that such appearance and participation will not unreasonably broaden the issues or burden the record, and otherwise may deny the application.

(3) This section does not apply to any person who might have been an original party in a proceeding before the commission if that person is required by statute to file a pleading or other response in the proceeding within a specified time.