As far as I know, there has not been any Supreme Court decision on a treaty provision that was in direct conflict with the Constitution (such as a treaty provision to ban the possession of private firearms which would directly conflict with the Second Amendment, or treaty provision providing for an ex post facto law or a bill of attainder against an individual).
Allow me to expand on my rather cryptic previous post by contradicting you ;)
Justice Black, for the Court:
At the time of Mrs. Covert's alleged offense, an executive agreement was in effect between the United States and Great Britain which permitted United States' military courts to exercise exclusive jurisdiction over offenses committed in Great Britain by American servicemen or their dependents. For its part, the United States agreed that these military courts would be willing and able to try and to punish all offenses against the laws of Great Britain by such persons. In all material respects, the same situation existed in Japan when Mrs. Smith killed her husband. 30 Even though a court-martial does not give an accused trial by jury and other Bill of Rights protections, the Government contends that Art. 2 (11) of the UCMJ, insofar as it provides for the military trial of dependents accompanying the armed forces in Great Britain and Japan, can be sustained as legislation which is necessary and proper to carry out the United States' obligations under the international agreements made with those countries. The obvious and decisive answer to this, of course, is that no agreement with a foreign nation can confer power on the Congress, or on any other branch of Government, which is free from the restraints of the Constitution.Article VI, the Supremacy Clause of the Constitution, declares:
"This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land;... ."There is nothing in this language which intimates that treaties and laws enacted pursuant to them do not have to comply with the provisions of the Constitution. Nor is there anything in the debates which accompanied the drafting and ratification of the Constitution which even suggests such a result. These debates as well as the history that surrounds the adoption of the treaty provision in Article VI make it clear that the reason treaties were not limited to those made in "pursuance" of the Constitution was so that agreements made by the United States under the Articles of Confederation, including the important peace treaties which concluded the Revolutionary War, would remain in effect. It would be manifestly contrary to the objectives of those who created the Constitution, as well as those who were responsible for the Bill of Rights — let alone alien to our entire constitutional history and tradition — to construe Article VI as permitting the United States to exercise power under an international agreement without observing constitutional prohibitions. In effect, such construction would permit amendment of that document in a manner not sanctioned by Article V. The prohibitions of the Constitution were designed to apply to all branches of the National Government and they cannot be nullified by the Executive or by the Executive and the Senate combined.
There is nothing new or unique about what we say here. This Court has regularly and uniformly recognized the supremacy of the Constitution over a treaty. For example, in Geofroy v. Riggs, 133 U.S. 258, 267 , it declared:
"The treaty power, as expressed in the Constitution, is in terms unlimited except by those restraints which are found in that instrument against the action of the government or of its departments, and those arising from the nature of the government itself and of that of the States. It would not be contended that it extends so far as to authorize what the Constitution forbids, or a change in the character of the government or in that of one of the States, or a cession of any portion of the territory of the latter, without its consent."This Court has also repeatedly taken the position that an Act of Congress, which must comply with the Constitution, is on a full parity with a treaty, and that when a statute which is subsequent in time is inconsistent with a treaty, the statute to the extent of conflict renders the treaty null. It would be completely anomalous to say that a treaty need not comply with the Constitution when such an agreement can be overridden by a statute that must conform to that instrument.
- Reid v. Covert, 354 U.S. 1 (1957)
Can you see such a decision made while paying hommage to international or other nations' laws? Such as Australia?, Britain? France? Germany? China? We would have to use them to keep them.