39 CFR 954.13: Appearances.

(a) The General Counsel of the Postal Service or a member of his or her staff designated by him or her shall represent the authorized official.

(b) A publisher or intervenor may appear and be heard in person or by attorney. Attorneys may practice before the Postal Service in accordance with applicable rules issued by the Judicial Officer. See part 951 of this chapter.

(c) An attorney representing a publisher or intervenor shall file a written authorization from the publisher or intervenor before he or she may participate in the proceeding. The publisher or intervenor must promptly file a notice of change of attorneys.

(d) When a publisher or intervenor is represented by an authorized attorney all subsequent pleadings shall be served upon the attorney.