U.S. Supreme Court McGrain v. Daugherty,  273 U.S. 135 (1927)  ::   https://supreme.justia.com/cases/federal/us/273/135/ 
  :: https://supreme.justia.com/cases/federal/us/273/135/#tab-opinion-1931647

 "... Thus, in McGrain v. Daugherty [1927], the U.S. Supreme Court was faced with a dispute rising from the "Teapot Dome scandal" under President Warren Harding. The scandal was a classic matter of legislative investigation. Secretary of the Interior Albert Bacon Fall stood accused of bribery after he leased Navy petroleum reserves at Teapot Dome in Wyoming and two other locations at bargain rates and did not put up the leases for competitive bidding. During this period, Congress pursued a wider range of alleged fraud and exercised oversight over the failure of the Administration to prosecute powerful figures and companies for violations under the Sherman and Clayton Acts. That investigation ultimately turned to the role of Attorney General Harry M. Daugherty and his brother (and Ohio bank president) Mally S. Daugherty.  Mally Daugherty refused to comply with a subpoena to testify and was arrested.  In referencing the “ample warrant for thinking, as we do,” the Supreme Court issued a resounding defense of congressional investigative authority, including compelling testimony from individuals and companies.  The Court held that “the power of inquiry-with process to enforce it-is an essential and appropriate auxiliary to the legislative function.” The Court emphasized that congressional authority to compel disclosures is necessary for committees to have a complete understanding of “the conditions which the legislation is intended to affect or change.” ..."