19 CFR § 145.59 - Seizures.
(a)Articles prohibited and contrary to law. All mail shipments containing articles the importation of which is prohibited, or articles imported into the United States in any manner contrary to law, shall be seized or detained as appropriate and held by Customs officers for appropriate treatment, except for certain articles which will be handled by the Postal Service as specified in §§ 145.51 and 145.52.
(b)Notification of seizure or detention. In all cases where articles are seized or detained by Customs officers, the addressee shall be notified of the seizure or detention, of the reason for such action, and, if appropriate, of his right to petition for relief (see part 171 of this chapter).