Discrimination against interstate commerce

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.