In the case of Western Union Telegraph Company v. Pennsylvania, the Supreme Court of the United States was asked to decide whether the state of Pennsylvania had the right to regulate the rates charged by the Western Union Telegraph Company for its services. The Court held that the state did have the right to regulate the rates, as the company was a public utility and was subject to the state's police power. The Court reasoned that the company was a public utility because it provided a service that was essential to the public, and that the state had the right to regulate the rates charged by the company in order to protect the public from excessive charges. The Court also held that the company was subject to the state's police power, which allowed the state to regulate the company's activities in order to protect the public from harm. The Court's decision in this case established the principle that states have the right to regulate the rates charged by public utilities in order to protect the public from excessive charges. This decision has been cited in numerous subsequent cases involving the regulation of public utilities.

In the dissenting opinion for Western Union Telegraph Company v. Pennsylvania, Justice Field argued that the state of Pennsylvania had no right to impose a tax on telegraph companies operating within its borders. He believed that such taxation was unconstitutional because it violated Article I, Section 8 of the Constitution which grants Congress exclusive power over interstate commerce and communication. Furthermore, he argued that if states were allowed to impose taxes on these activities then they would be able to interfere with interstate commerce in ways not intended by Congress or authorized by law. Finally, he noted that while some forms of taxation may be necessary for public purposes, this particular form was excessive and unnecessary given how much money already generated from other sources like postage stamps and fees charged for services rendered.