No party or representative of a party involved in a proceeding before an administrative judge or Reviewing Board shall submit to the administrative judge or Reviewing Board any information, evidence, argument, or advice, whether written or oral, regarding any matter at issue in such proceeding unless such submission is part of the record or made in the presence of all parties. When a party to a proceeding submits a letter or any writing to an administrative judge or the Reviewing Board, a copy shall be served by mail or in hand on counsel for each other party or directly on each other party if not represented.