First, it bears noting that the statutory language of section 6103(f) is unambiguous and raises no complicated legal issues that warrant supervision or review by the Department of the Treasury (“Treasury”) or the Department of Justice (“Justice”). Section 6103(f) commands that “[u]pon written request from the chairman of the Committee on Ways and Means of the House of Representatives . . . the Secretary shall furnish such committee with any return or return information specified in such request.” 26 U.S.C. § 6103(f)(1) (emphasis added). It is a well-established principle of statutory interpretation that words that are neither terms of art nor statutorily defined be given their ordinary meaning. Here, the statute’s use of the “mandatory ‘shall’ . . . creates an obligation impervious to judicial discretion.” Lexecon, Inc. v. Milberg Weiss Bershad Hynes & Lerach, 523 U.S. 26, 35 (1998); see also, e.g., EPA v. EME Homer City Generation, 572 U.S. 489, 509 (2014); Barnhart v. Sigmon Coal Co., 534 U.S. 438, 461-62 (2002) (courts “must presume that a legislature says in a statute what it means and means in a statute what it says there.” (internal quotation marks omitted)).

Second, there is no valid basis to question the legitimacy of the Committee’s legislative purpose here. The Supreme Court has instructed that Congress’s power to investigate is “broad” and “encompasses inquiries concerning the administration of existing laws as well as proposed or possibly needed statutes.” Watkins v. United States, 354 U.S. 178, 187 (1957).

….