In the exercise of its power to regulate interstate and foreign commerce, Congress has enacted statutes which need not be here discussed in detail. It has in a variety of ways regulated the commerce on navigable rivers and lakes. It has regulated railroad transportation for the purpose of preventing unjust discrimination in rates as between persons and localities, and has provided (1887) for an interstate commerce commission, having specific duties to perform with reference to the enforcement of these laws. It has also exercised incidentally a police power over interstate commerce (see above, § 49) as by prohibiting the transportation from one state to another of lottery tickets, thus extending the power to regulate so as to amount to entire exclusion (Lottery Case). It has passed statutes as to immigration and in a variety of ways regulated and exercised supervision over commerce on the high seas either with foreign countries or between ports of the different states.

In the further exercise of its powers as to interstate and foreign commerce, Congress has by the so-called Sherman Act of 1890 prohibited the making of contracts and the formation of trusts and combinations and every other attempt to monopolize such commerce, and by a statute of 1898 made provision for settlement of controversies between carriers engaged in such commerce and their employes. As to the Sherman Act it has been decided that while the manufacturer of goods to be shipped into another state or abroad is not within the control of Congress (United States v. E. C. Knight Co.) the consolidation of competing railroad lines by means of the organization of a corporation to hold and control the stock of the railroad companies forming such lines so as to completely pool their interests and take over all inducement for competition is an arrangement in restraint of trade and an attempt to form a monopoly, and is invalid (Northern Securities Co. v. United States). Congress has power under the commerce clause of the Constitution to restrict and regulate the use of every instrumentality employed in interstate or international commerce, so far as it may be necessary to do so in order to prevent the restraint thereof denounced by the Anti Trust Act ( United States v. Standard Oil Co.). Several other important decisions have been rendered as to the validity and effect of that statute, but they are all referred to and commented on in the case last above cited. For the purpose of preventing discrimination in rates of transportation in interstate commerce Congress has passed an act (1903) making it a crime for a carrier to transport merchandise at less than its published rate. (Armour Packing Co. v. United States).

The power of Congress to regulate commerce has been held to extend to the preservation of the navigability of rivers and lakes within state limits, and in the exercise of this power Congress may prohibit the construction of dams or the diversion of water, even at points above the head of navigation of a navigable stream, so as to preserve the flow of water in that portion of the stream which is capable of use for the purpose of navigation (United States v. Rio Grande Dam and Irrigation Co. and Kansas v. Colorado) .

In the exercise of its power to regulate commerce with the Indian tribes Congress has prohibited the sale of intoxicating liquors to the members of such tribes, and in other ways sought to protect them from impositions or injury at the hands of white persons seeking to take advantage of their helpless condition. And it has been held (United States v. Holiday) that such statutes may be made applicable to commercial transactions between the members of Indian tribes and white persons, whether such transactions take place on Indian reservations or elsewhere.

But the control which the federal government may exercise over such commerce as is placed under the regulation of Congress is not limited to the enactment of statutes. The federal executive may act, even to the extent of employing the military power to prevent unlawful interference with such commerce, as he may in preventing interruption in the carrying of the mails, and injunction suits may be prosecuted under his authority to stop any such interference. This power was exercised by President Cleveland in 1894 on the occasion of the so-called "Pullman Strike," and was sustained by the Supreme Court in the Debs Case,