51 Pa. Code § 13.4 – Intervention.

(a) A person who is not a party in an advice or opinion request or reconsideration thereof, may file a petition to intervene if the person has an interest. One or more of the following criteria will be utilized to determine whether a person has an interest:
1. (1) A right conferred by Federal or State law.
2. (2) An interest which may be affected and which is not adequately represented.
3. (3) An issue of public importance.
(b) A person shall apply for intervention within 14 days prior to the Commission meeting if the opinion will be reviewed or decided. The Commission may grant an application at any time prior to the meeting, but only for good cause shown.
(c) An application for intervention shall include the facts which establish the nature of the alleged right or interest and the grounds for intervention. The application shall also address the facts if they are deficient or incorrectly stated, and the relevant issues of law. The application may cite authority in support of the advocated position.
(d) The Commission will review applications for intervention to determine whether a grant of intervention is appropriate.
(e) A person may file an amicus brief which shall be received within 14 days prior to the Commission meeting.