Article I, Section 8, Clause 3:
[The Congress shall have Power . . .] To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes; . . .
The earliest acts prohibiting commerce were in the nature of quarantine regulations and usually dealt solely with interstate transportation. In 1884, the exportation or shipment in interstate commerce of livestock having any infectious disease was forbidden. 1 In 1903, power was conferred upon the Secretary of Agriculture to establish regulations to prevent the spread of such diseases through foreign or interstate commerce. 2 In 1905, the same official was authorized to lay an absolute embargo or quarantine upon all shipments of cattle from one state to another when the public necessity might demand it. 3 A statute passed in 1905 forbade the transportation in foreign and interstate commerce and the mails of certain varieties of moths, plant lice, and other insect pests injurious to plant crops, trees, and other vegetation. 4 In 1912, a similar exclusion of diseased nursery stock was decreed, 5 while by the same act and again by an act of 1917, 6 the Secretary of Agriculture was invested with powers of quarantine on interstate commerce for the protection of plant life from disease similar to those above described for the prevention of the spread of animal disease. Although the Supreme Court originally held federal quarantine regulations of this sort to be constitutionally inapplicable to intrastate shipments of livestock, on the ground that federal authority extends only to foreign and interstate commerce, 7 this view has today been abandoned.