In the 1926 case of McGrain v. Daugherty, the U.S. Supreme Court upheld Congress's power to compel testimony for legislative purposes. The Senate had launched an investigation into Attorney General Harry M. Daugherty's failure to prosecute certain alleged violations of law during President Warren G Harding’s administration and subpoenaed his brother, Mally S. Daugherty, who was a bank president in Ohio where some suspicious transactions occurred related to these allegations. When he refused to appear before the committee or produce requested documents on grounds that they were outside congressional jurisdiction, he was arrested by Senate Sergeant at Arms John Jurney under contempt charges. The case reached the Supreme Court which ruled in favor of Congress with Justice Van Devanter writing for a unanimous court that "the power of inquiry—with process to enforce it—is an essential and appropriate auxiliary to the legislative function." He further clarified that while this power is not explicitly mentioned in constitution but it was implicit as it is necessary for legislature’s functions such as legislation and impeachment among others.

In the dissenting opinion for McGrain v. Daugherty, it was argued that the Senate overstepped its constitutional boundaries by issuing a subpoena to Mally S. Daugherty. The dissenting justices believed that this action violated the separation of powers as outlined in the Constitution because it allowed a legislative body (the Senate) to exercise judicial power. They contended that while Congress does have broad investigative powers, these should be limited to inquiries related to legislation or impeachment proceedings - neither of which were relevant in this case. Furthermore, they expressed concern about potential abuses of power and violations of individual rights if such expansive interpretation of congressional authority was permitted without clear constitutional basis or limits.