At no time after a respondent has requested an on-the-record adjudication of the assessment of a civil penalty shall a DOE Official, or any person who is likely to advise a DOE Official in the decision on the case, discuss ex parte the merits of the proceeding with any interested person outside DOE, with any DOE staff member who performs 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 a DOE Official during the pendency of the proceeding and relating to the merits thereof, by or on behalf of any party shall be regarded as argument made in the proceeding and shall be served upon all other parties. Any oral communication shall be set forth in a written memorandum and served on all other parties. The other parties shall be given an opportunity to reply to such memorandum or communication.