19 USC 1486 - Administration of oaths

(a) Customs officers 
The following officers and employees may administer any oaths required or authorized by law or regulations promulgated thereunder in respect of any matter coming before such officers or employees in the performance of their official duties:
(1)  Any customs officer appointed by the President;
(2)  the chief assistant of any such officer, or any officer or employee of the customs field service designated for the purpose by such officer or by the Secretary of the Treasury; and
(3)  any officer or employee of the United States Customs Service designated for the purpose by the Secretary of the Treasury.
(b) Postmasters 
The postmaster or assistant postmaster of the United States at any post office where customs officers are not stationed, is authorized to administer any oaths required to be made to statements in customs documents by importers of merchandise, not exceeding $100 in value, through the mails.
(c) No compensation 
No compensation or fee shall be demanded or accepted for administering any oath under the provisions of this section.
(d) Verification in lieu of oath 
The Secretary of the Treasury may by regulation prescribe that any document required by any law administered by the Customs Service to be under oath may be verified by a written declaration in such form as he shall prescribe, such declaration to be in lieu of the oath otherwise required.