United States v. Philadelphia and Reading Railroad Company is a United States Supreme Court case that dealt with the issue of whether the federal government had the power to regulate the rates of a railroad company. The case arose when the Philadelphia and Reading Railroad Company refused to comply with the Interstate Commerce Commission's order to reduce its freight rates. The company argued that the federal government did not have the power to regulate its rates, and that the power to regulate rates was reserved to the states. The Supreme Court held that the federal government did have the power to regulate the rates of the railroad company. The Court reasoned that the power to regulate interstate commerce was granted to the federal government by the Constitution, and that the power to regulate the rates of a railroad company was an inherent part of the power to regulate interstate commerce. The Court also held that the power to regulate interstate commerce was exclusive to the federal government, and that the states did not have the power to regulate the rates of a railroad company. In conclusion, the Supreme Court held that the federal government had the power to regulate the rates of the Philadelphia and Reading Railroad Company, and that the power to regulate interstate commerce was exclusive to the federal government.

In United States v. Philadelphia and Reading Railroad Company, the Supreme Court was tasked with determining whether or not Congress had the authority to impose a tax on railroad companies in order to fund pensions for Civil War veterans. The majority opinion held that Congress did have this power under its taxing authority granted by Article I of the Constitution. However, Justice Field dissented from this opinion, arguing that such a tax would be unconstitutional because it violated both due process and equal protection clauses of the Fourteenth Amendment. He argued that since there is no direct connection between railroads and pensioners, any taxation imposed upon them would be arbitrary and unjustified discrimination against certain businesses without any rational basis for doing so. Furthermore, he argued that such taxation could also lead to an unequal burden being placed on different states depending on their respective number of railroads within their borders; thus violating equal protection principles as well as state sovereignty rights guaranteed by the Tenth Amendment.