29 CFR 459.4: Service of pleading and other papers under this subchapter.

(a) Method of service. Notices of hearing, decisions, orders and other papers may be served personally or by registered or certified mail or by telegraph. When service is by mail, the date of service shall be the day when the matter served is deposited in the United States mail.

(b) Upon whom served. All papers, except as herein otherwise provided, shall be served upon all counsel of record and upon parties not represented by counsel or by their agents designated by them or by law and upon the Director, or his designated officer, or agent or Administrative Law Judge where appropriate. Service upon such counsel or representative shall constitute service upon the party, but a copy also shall be transmitted to the party.