H.P. Hood & Sons, Inc. (plaintiff) was a Massachusetts company that distributed milk and milk products to Boston. In addition to the milk it received from Hood and other milk producers, Boston received approximately 8 percent of its milk supply from producers located in New York. Hood had three milk-receiving plants in New York and sought to open an additional milk plant in Greenwich, New York. Hood wanted to open the new plant because its existing milk-receiving plants were having difficulty handling milk in the time required by the Boston health authorities. Du Mond (defendant), the Commissioner of Agriculture & Markets of New York, denied Hood’s application for a license to build the new plant. Du Mond sought to promote the sale of milk from in-state New York producers by denying the building of a new plant by an out-of-state milk producer. Du Mond found, among other things, that Hood's new plant would divert supply from other in-state producers and subject in-state producers to competition. The lower courts upheld New York’s denial of Hood’s application to build a new plant, and the United States Supreme Court granted certiorari.