Whitney (plaintiff), a merchant engaged in importing sugar to the United States from the Dominican Republic brought suit against Robertson (defendant), a United States Customs official, arguing that he should not be required to pay duties on the sugar because his product was similar to sugar being imported duty-free into the United States from the Hawaiian Islands. In making this argument, Whitney cited a treaty between the United States and the Dominican Republic which guaranteed that no higher duty would be imposed on goods imported by the United States from the Dominican Republic than on goods imported from any other country. However, an act of Congress also existed which authorized the collection of these duties on goods imported from the Dominican Republic. The statute was passed after the United States entered into its treaty with the Dominican Republic. The lower court held for Robertson, and Whitney appealed.