Except as otherwise provided by the Secretary, any return, declaration, statement, or other document required to be made under any provision of the internal revenue laws or regulations shall contain or be verified by a written declaration that it is made under the penalties of perjury.
26 U.S. Code § 6065 - Verification of returns
1976—Pub. L. 94–455, § 1906(a)(6), struck out provisions relating to the authority of the Secretary or his delegate to require that any return, statement, or other document to be made under provision of the internal revenue laws or regulations shall be verified by an oath.
Pub. L. 94–455, § 1906(b)(13)(A), struck out “or his delegate” after “Secretary”.