40 CFR 305.7: Ex parte discussion of proceeding.

At no time after the Request for a Hearing is referred to the Presiding Officer shall the Presiding Officer discuss ex parte the merits of the proceeding with any interested person outside the Agency, with any Agency staff member who performed a prosecutorial or investigative function in such proceeding or a factually related proceeding, or with any representative of such person. Any ex parte memorandum or other communication addressed to the Presiding Officer 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 and shall be served upon all other parties. Any other party shall be given the opportunity to reply to such memorandum or communication.