Relationship of international law and municipal law — Treaties — Effect in municipal law — United States — Treaties part of United States law — Act of Congress potentially in conflict with prior treaty obligation — Interpretation of statute — Presumption that Congress did not intend to legislate in a manner contrary to treaty obligations — Scope of presumption — Whether presumption applicable only when legislation having effect of abrogating Treaty — Presumption that Congress did not intend to legislate in a manner contrary to the law of nations — General Agreement on Tariffs and Trade — Canada-United States Free Trade Agreement — United States Poultry Protection Inspection Act

Relationship of international law and municipal law — Conduct of foreign relations — Role of the Executive and the courts — Executive branch having exclusive authority over the conduct of foreign affairs — Whether foreign affairs including foreign commerce

Economics, trade and finance — Multilateral trade agreements — Conflict with municipal legislation — Whether municipal legislation taking precedence — Whether multilateral trade agreements constituting part of the law of nations — General Agreement on Tariffs and Trade — Canada-United States Free Trade Agreement

Sources of international law — Multilateral trade agreements — Whether constituting part of the law of nations

Treaties — Whether prevailing over conflicting municipal legislation — The law of the United States