Whitney v. Robertson

In 1861, the United States & the Dominican Republic ("San Domingo") entered into a treaty with respect to trade. One provision was that the United States would charge the Dominican Republic an import tax higher than what it charges other nations.

In 1870, the United States Congress passed a Customs Act; this Act imposes an import duty on all foreign sugar & molasses regardless of provenance.

In 1875, the United States and the Kingdom of Hawaii entered into a duty-free sugar & molasses treaty

In 1882, Whitney (plaintiff) and others imported sugar into the United States from San Domingo. Robertson (defendant) was a Customs Official at a New York port who demanded duty payments based on the latest U.S. federal statute.

The U.S. Secretary of the Treasury agreed with Robertson that imports of sugar from San Domingo shouldn't be duty-free.

When happens when a treaty and federal law are in discord?

A federal statute enacted last takes precedence over a treaty entered into earlier.

Here, the 1870 Customs Act of Congress overrides the 1861 treaty.

Both treaties and congressional acts are the supreme laws of the United States. The latest one takes precedence.