commercial intercourse from local control. Gibbons v. Ogden, 9 Wheat. 1, 196, 224; Brown v. Maryland, 12 Wheat. 419, 446; County of Mobile v. Kimball, 102 U. S. 691, 696, 697; Smith v. Alabama, 124 U. S. 45, 473; Second Employers' Liability Cases, 223 U. S. 1, 47, 53, 54; Minnesota Rate Cases, 230 U. S. 352, 398, 399.

Congress is empowered to regulate, that is, to provide the law for the government of interstate commerce; to enact 'all appropriate legislation' for its 'protection and advancement' (The Daniel Ball, 10 Wall. 557, 564); to adopt measures 'to promote its growth and insure its safety' (County of Mobile v. Kimball, supra); 'to foster, protect, control and restrain' (Second Employers' Liability Cases, supra). Its authority, extending to these interstate carriers as instruments of interstate commerce, necessarily embraces the right to control their operations in all matters having such a close and substantial relation to interstate traffic that the control is essential or appropriate to the security of that traffic, to the efficiency of the interstate service, and to the maintenance of conditions under which interstate commerce may be conducted upon fair terms and without molestation or hindrance. As it is competent for Congress to legislate to these ends, unquestionably it may seek their attainment by requiring that the agencies of interstate commerce shall not be used in such manner as to cripple, retard or destroy it. The fact that carriers are instruments of intrastate commerce, as well as of interstate commerce, does not derogate from the complete and paramount authority of Congress over the latter or preclude the Federal power from being exerted to prevent the intrastate operations of such carriers from being made a means of injury to that which has been confided to Federal care. Wherever the interstate and intrastate transactions of carriers are so related that the government of the one involves the control of the other, it is Congress, and not the State, that is entitled to pre

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scribe the final and dominant rule, for otherwise Congress would be denied the exercise of its constitutional authority and the State, and not the Nation, would be supreme within the national field. Baltimore & Ohio Railroad Co. v. Interstate Commerce Commission, 221 U. S. 612, 618; Southern Railway Co. v. United States, 222 U. S. 20, 26, 27; Second Employers' Liability Cases, supra, pp. 48, 51; Interstate Commerce Commission v. Goodrich Transit Co., 224 U. S. 194, 205, 213; Minnesota Rate Cases, supra, p. 431; Illinois Central Railroad Co. v. Behrens, 233 U. S. 473.

In Baltimore & Ohio Railroad Co. v. Interstate Commerce Commission, supra, the argument against the validity of the Hours of Service Act (March 4, 1907, c. 2939, 34 Stat. 1415) involved the consideration that the interstate and intrastate transactions of the carriers were so interwoven that it was utterly impracticable for them to divide their employés so that those who were engaged in interstate commerce should be confined to that commerce exclusively. Employés dealing with the movement of trains were employed in both sorts of commerce; but the court held that this fact did not preclude the exercise of Federal power. As Congress could limit the hours of labor of those engaged in interstate transportation, it necessarily followed that its will could not be frustrated by prolonging the period of service through other requirements of the carriers or by the commingling of duties relating to interstate and intrastate operations. Again, in Southern Railway Co. v. United States, supra, the question was presented whether the amendment to the Safety Appliance Act (March 2, 1903, c. 976, 32 Stat. 943) was within the power of Congress in view of the fact that the statute was not confined to vehicles that were used in interstate traffic but also embraced those used in intrastate traffic. The court answered affirmatively, because there was such a close relation between the two classes of traffic moving over the same railroad as to make it certain that the safety

of the interstate traffic, and of those employed in its movement, would be promoted in a real and substantial sense by applying the requirements of the act to both classes of vehicles. So, in the Second Employers' Liability Cases, supra, it was insisted that while Congress had the authority to regulate the liability of a carrier for injuries sustained by one employé through the negligence of another, where all were engaged in interstate commerce, that power did not embrace instances where the negligent employé was engaged in intrastate commerce. The court said that this was a mistaken theory, as the causal negligence when operating injuriously upon an employé engaged in interstate commerce had the same effect with respect to that commerce as if the negligent employé were also engaged therein. The decision in Employers' Liability Cases, 207 U. S. 463, is not opposed, for the statute there in question (June 11, 1906, c. 3073, 34 Stat. 232) sought to regulate the liability of interstate carriers for injuries to any employé even though his employment had no connection whatever with interstate commerce. (See Illinois Central R. R. Co. v. Behrens, supra.)

While these decisions sustaining the Federal power relate to measures adopted in the interest of the safety of persons and property, they illustrate the principle that Congress in the exercise of its paramount power may prevent the common instrumentalities of interstate and intrastate commercial intercourse from being used in their intrastate operations to the injury of interstate commerce. This is not to say that Congress possesses the authority to regulate the internal commerce of a State, as such, but that it does possess the power to foster and protect interstate commerce, and to take all measures necessary or appropriate to that end, although intrastate transactions of interstate carriers may thereby be controlled.

This principle is applicable here. We find no reason to doubt that Congress is entitled to keep the highways of VOL. CCXXXIV-23

Opinion of the Court.

234 U. S.

interstate communication open to interstate traffic upon fair and equal terms. That an unjust discrimination in the rates of a common carrier, by which one person or locality is unduly favored as against another under substantially similar conditions of traffic, constitutes an evil is undeniable; and where this evil consists in the action of an interstate carrier in unreasonably discriminating against interstate traffic over its line, the authority of Congress to prevent it is equally clear. It is immaterial, so far as the protecting power of Congress is concerned, that the discrimination arises from intrastate rates as compared with interstate rates. The use of the instrument of interstate commerce in a discriminatory manner so as to inflict injury upon that commerce, or some part thereof, furnishes abundant ground for Federal intervention. Nor can the attempted exercise of state authority alter the matter, where Congress has acted, for a State may not authorize the carrier to do that which Congress is entitled to forbid and has forbidden.

It is also to be noted-as the Government has well said in its argument in support of the Commission's order-that the power to deal with the relation between the two kinds of rates, as a relation, lies exclusively with Congress. It is manifest that the State cannot fix the relation of the carrier's interstate and intrastate charges without directly interfering with the former, unless it simply follows the standard set by Federal authority. This question was presented with respect to the long and short haul provision of the Kentucky constitution, adopted in 1891, which the court had before it in Louisville & Nashville R. R. Co. v. Eubank, 184 U. S. 27. The state court had construed this provision as embracing a long haul, from a place outside to one within the State, and a shorter haul on the same line and in the same direction between points within the State. This court held that, so construed, the provision was invalid as being a regulation of interstate commerce

because 'it linked the interstate rate to the rate for the shorter haul and thus the interstate charge was directly controlled by the state law.' See 230 U. S. pp. 428, 429. It is for Congress to supply the needed correction where the relation between intrastate and interstate rates presents the evil to be corrected, and this it may do completely by reason of its control over the interstate carrier in all matters having such a close and substantial relation to interstate commerce that it is necessary or appropriate to exercise the control for the effective government of that commerce.

It is also clear that, in removing the injurious discriminations against interstate traffic arising from the relation of intrastate to interstate rates, Congress is not bound to reduce the latter below what it may deem to be a proper standard fair to the carrier and to the public. Otherwise, it could prevent the injury to interstate commerce only by the sacrifice of its judgment as to interstate rates. Congress is entitled to maintain its own standard as to these rates and to forbid any discriminatory action by interstate carriers which will obstruct the freedom of movement of interstate traffic over their lines in accordance with the terms it establishes.

Having this power, Congress could provide for its execution through the aid of a subordinate body; and we conclude that the order of the Commission now in question cannot be held invalid upon the ground that it exceeded the authority which Congress could lawfully confer.

Second. The remaining question is with regard to the scope of the power which Congress has granted to the Commission.

Section three of the Act to Regulate Commerce provides (February 4, 1887, c. 104, 24 Stat. 379, 380):

"SEC. 3. That it shall be unlawful for any common carrier subject to the provisions of this act to make or give any undue or unreasonable preference or advantage to