(a) After an order, decision, report, or action has been made or taken in any proceeding by the Commission, or by any designated authority within the Commission pursuant to a delegation under section 155(c)(1) of this title, any party thereto, or any other person aggrieved or whose interests are adversely affected thereby, may petition for reconsideration only to the authority making or taking the order, decision, report, or action; and it shall be lawful for such authority, whether it be the Commission or other authority designated under section 155(c)(1) of this title, in its discretion, to grant such a reconsideration if sufficient reason therefor be made to appear. A petition for reconsideration must be filed within thirty days from the date upon which public notice is given of the order, decision, report, or action complained of. No such application shall excuse any person from complying with or obeying any order, decision, report, or action of the Commission, or operate in any manner to stay or postpone the enforcement thereof, without the special order of the Commission. The filing of a petition for reconsideration shall not be a condition precedent to judicial review of any such order, decision, report, or action, except where the party seeking such review (1) was not a party to the proceedings resulting in such order, decision, report, or action, or (2) relies on questions of fact or law upon which the Commission, or designated authority within the Commission, has been afforded no opportunity to pass. The Commission, or designated authority within the Commission, shall enter an order, with a concise statement of the reasons therefor, denying a petition for reconsideration or granting such petition, in whole or in part, and ordering such further proceedings as may be appropriate: Provided, That in any case where such petition relates to an instrument of authorization granted without a hearing, the Commission, or designated authority within the Commission, shall take such action within ninety days of the filing of such petition. Reconsiderations shall be governed by such general rules as the Commission may establish, except that no evidence other than newly discovered evidence, evidence which has become available only since the original taking of evidence, or evidence which the Commission or designated authority within the Commission believes should have been taken in the original proceeding shall be taken on any reconsideration. The time within which a petition for review must be filed in a proceeding to which section 402(a) of this title applies, or within which an appeal must be taken under section 402(b) of this title in any case, shall be computed from the date upon which the Commission gives public notice of the order, decision, report, or action complained of.

(b)

(1) Within 90 days after receiving a petition for reconsideration of an order concluding a hearing under section 204(a) of this title or concluding an investigation under section 208(b) of this title, the Commission shall issue an order granting or denying such petition.

(2) Any order issued under paragraph (1) shall be a final order and may be appealed under section 402(a) of this title.