While in the Senate, Pepper maintained a reduced private practice. The cases of which he was most proud of during that time were Frick v. Pennsylvania, an inheritance tax case, and Myers v. United States, which he argued as amicus curiae at the invitation of the Supreme court, concerning President Wilson's removal of a postmaster. Although the Court decided that the legislative act requiring Senatorial consent to such removal was unconstitutional, it thanked him for his service and he believed the decision vindicated President Andrew Johnson's position with respect to the Tenure of Office Act, and that the powerful dissent by Justices Holmes, McReynolds and Brandeis might eventually receive favorable future reconsideration. Pepper also took pride in his handling of the George Otis Smith case (concerning the Federal Power Commission), where Pepper vindicated Presidential rights against the Senate, having refused a senatorial delegation's offer to represent them but accepting that of Attorney General Mitchell.