40 C.F.R. § 164.7
At no stage of a proceeding shall the Administrator, the members of the Environmental Appeals Board, the Presiding Officer, or the Administrative Law Judge discuss ex parte the merits of the proceeding with any party or with any person who has been connected with the preparation or presentation of the proceeding as an advocate, or in an investigative or expert capacity, or with any representative of such person, Provided, That the Environmental Appeals Board, the Presiding Officer, or the Administrative Law Judge may discuss the merits of the case with any such person if all parties to the proceeding, or their representatives, have been given reasonable notice and opportunity to be present. Any memorandum or other communication addressed to the Administrator, the Environmental Appeals Board, the Presiding Officer, or the Administrative Law Judge during the pendency of the proceeding, and relating to the merits thereof, by or on behalf of any party, shall be regarded as an argument made in the proceeding. The Administrator, the Environmental Appeals Board, the Presiding Officer, or the Administrative Law Judge shall cause any such communication to be filed with the hearing clerk and served upon all other parties to the proceeding who will be given the opportunity to file an answer thereto.
40 C.F.R. §164.7