U.S. v. Nixon (1974)
The Court held that the president could not claim “executive privilege” in order to avoid a subpoena to produce taped communications among members of his staff. By refusing to produce the tapes, President Nixon had exceeded his power under Article II of the Constitution. “Neither the doctrine of separation of powers, nor the need for confidentiality of high-level communications, without more, can sustain an absolute, unqualified Presidential privilege of immunity from judicial process under all circumstances.”
Moreover, the Court explained that its decision “unequivocally reaffirmed the holding of Marbury v. Madison... that ‘it is emphatically the province and duty of the judicial department to say what the law is.’”
The case touched on constitutional principles including checks and balances and limited government.