29 CFR 503.41: Administrator, WHD's determination.

(a) Whenever the Administrator, WHD decides to assess a civil money penalty, to debar, or to impose other appropriate administrative remedies, including for the recovery of monetary relief, the party against which such action is taken will be notified in writing of such determination.

(b) The Administrator, WHD's determination will be served on the party by personal service or by certified mail at the party's last known address. Where service by certified mail is not accepted by the party, the Administrator may exercise discretion to serve the determination by regular mail.