A petition for reopening for the purpose of rehearing, reargument, or reconsideration, shall be made in writing, shall state the grounds relied upon, and conform to the requirements of subpart D of this part. If the petition is for the purpose of rehearing, said petition shall state the nature and purpose of the new evidence to be adduced and that such evidence was not available at the time of the prior hearing. If the petition be for reargument or reconsideration, the matter claimed to have been erroneously decided shall be specified and the alleged errors briefly stated. In case of exceptional circumstances, satisfactorily shown by the petitioner, a request for modification of rules or orders may be made by telegram or otherwise, upon notice to all parties or attorneys of record, but such request shall be followed by a petition filed and served in accordance with subpart D of this part.