(a) Any interested person or organization may file a petition to participate in a proceeding as an amicus curiae. Such petition shall be filed prior to the prehearing conference, or if none is held, before the commencement of the hearing, unless the petitioner shows good cause for filing the petition later. The presiding officer may grant the petition if he finds that the petitioner has a legitimate interest in the proceedings, that such participation will not unduly delay the outcome, and may contribute materially to the proper disposition thereof. An amicus curiae is not a party and may not introduce evidence at a hearing.

(b) An amicus curiae may submit a statement of position to the presiding officer prior to the beginning of a hearing, and shall serve a copy on each party. The amicus curiae may submit a brief on each occasion a decision is to be made or a prior decision is subject to review. His brief shall be filed and served on each party within the time limits applicable to the party whose position he deems himself to support; or if he does not deem himself to support the position of any party, within the longest time limit applicable to any party at that particular stage of the proceedings.

(c) When all parties have completed their initial examination of a witness, any amicus curiae may request the presiding officer to propound specific questions to the witness. The presiding officer, in his discretion, may grant any such request if he believes the proposed additional testimony may assist materially in elucidating factual matters at issue between the parties and will not expand the issues.