26 U.S.C. § 7622

(a) Internal revenue personnel Every officer or employee of the Treasury Department designated by the Secretary for that purpose is authorized to administer such oaths or affirmations and to certify to such papers as may be necessary under the internal revenue laws or regulations made thereunder. (b) Others Any oath or affirmation required or authorized under any internal revenue law or under any regulations made thereunder may be administered by any person authorized to administer oaths for general purposes by the law of the United States, or of any State or possession of the United States, or of the District of Columbia, wherein such oath or affirmation is administered. This subsection shall not be construed as an exclusive enumeration of the persons who may administer such oaths or affirmations.