29 CFR § 6.3 - Service; copies of documents and pleadings.
(a) Manner of service. Service upon any party shall be made by the party filing the pleading or document by delivering a copy or mailing a copy to the last known address. When a party is represented by an attorney, the service should be upon the attorney.
(b) Proof of service. A certificate of the person serving the pleading or other document by personal delivery or by mailing, setting forth the manner of said service shall be proof of the service. Where service is made by mail, service shall be complete upon mailing. However, documents are not deemed filed until received by the Chief Clerk at the Office of Administrative Law Judges and where documents are filed by mail 5 days shall be added to the prescribed period.
(c) Service upon Department, number of copies of pleading or other documents. An original and three copies of all pleadings and other documents shall be filed with the Department of Labor: The original and one copy with the Administrative Law Judge before whom the case is pending, one copy with the attorney representing the Department during the hearing, and one copy with the Associate Solicitor.