28 CFR 76.6 - Service and filing of documents.
(a) Generally. Unless ordered otherwise, an original and one copy of the complaint and all other pleadings shall be filed with the Judge who has been assigned to the case. Each party shall deliver or mail, in accordance with paragraph (b) of this section, a copy of all pleadings, including any attachments to the other party. Each pleading filed shall be clear and legible.
(b) By and on parties. The Notice of Intent to Assess Civil Penalty and the Complaint shall be served by personal delivery or by certified or registered mail, return receipt requested, to the respondent. When it is known that a party is represented by an attorney, service of any other pleading, paper or document subsequent to the Notice and Complaint shall be made upon the party's attorney. Service of such other pleadings, papers, or documents may be made by personal delivery or by mailing, by first class mail, a copy to the party or attorney at the party's or attorney's last known address. The party serving the document shall certify the manner and date of service.
(c) By the judge. Except as provided in paragraph (d) of this section, service of Notices, Orders and Decisions shall be made by first class mail to the last known address of a party or, if the party is known to be represented by an attorney, to the attorney.
(d) Service of notice of hearing. Service of Notice of the Date Set for Hearing shall be made by the Judge with whom the complaint has been filed either by delivering a copy to the individual party or, if known, to the attorney of record of a party; or by mailing, by certified or registered mail, return receipt requested, a copy to the last known address of a party or a party's attorney.
(e) Service is complete upon delivery to the addressee or, in the case of service by mail, upon mailing.