See 26 U.S.C.§ 7602, which provides (in part): "For the purpose of ascertaining the correctness of any return [or] determining the liability of any person for any internal revenue tax [ . . . ], or collecting any such liability, the Secretary [of the Treasury or his delegate] is authorized—(1) To examine any books, papers, records, or other data which may be relevant or material to such inquiry; (2) To summon the person liable for tax or required to perform the act, or any officer or employee of such person, or any person having possession, custody, or care of books of account [ . . . ] to appear before the Secretary [of the Treasury or his delegate . . . ] and to produce such books, papers, records, or other data, and to give such testimony, under oath, as may be relevant or material to such inquiry [ . . . . ]"
