The Constitution grants to Congress the power "To regulate Commerce with foreign Nations, and among the several States.…" A few cases in the 1800s indicated that the power to regulate foreign commerce was the same as the power to regulate interstate commerce. Later, in Brolan v. United States (1915), the Supreme Court indicated that the power given Congress to regulate foreign commerce was so complete that it was limited only by other portions of the Constitution. So the Court upheld Congress in its regulating, prohibiting, and taxing commerce with other nations while sometimes restricting its power to regulate interstate commerce.
Today the issue is of no significance. The power of Congress to regulate interstate commerce is so great as to make any distinctions meaningless. Congress need only concern itself with the specific constitutional restrictions on the foreign commercial power: those preventing the taxation of exports and giving any preference to the ports of one state over those of another state.
In Japan Line, Ltd. v. Los Angeles (1979), however, the Court held that the foreign commerce clause may serve to limit state taxation in cases in which the interstate commerce clause would not. The Court held invalid a nondiscriminatory, apportioned, state property tax on the value of shipping containers belonging to a Japanese shipping company. The Court said that the tax would have been valid if it had been applied to interstate shipments, but was not here because the containers were taxed on full value in Japan and the Court had no authority to require apportioned taxation in foreign lands. The Court said that state taxes on foreign commerce had to meet all the tests for interstate commerce; in addition, the Court must inquire whether even with apportionment a substantial risk of international multiple taxation persists, and whether the tax prevents the federal government from speaking with one voice when regulating commerce with foreign governments.
Edward L. Barrett, Jr.
Henkin, Louis 1972 Foreign Affairs and the Constitution. Pages 69–71. Mineola, N.Y.: Foundation Press.