The U.S. Supreme Court case Western Union Telegraph Co. v. Pennsylvania in 1961 revolved around the issue of whether or not a state could tax interstate telegraph messages under the Due Process and Commerce Clauses of the Constitution. The State of Pennsylvania had imposed a tax on all telegraphic messages sent from within its borders, regardless if they were destined for another state or country, which was challenged by Western Union Telegraph Company as unconstitutional interference with interstate commerce and violation of due process rights. In this case, the court ruled in favor of Pennsylvania stating that such taxation did not violate either clause because it was applied to an activity (sending telegrams) occurring entirely within its jurisdictional boundaries even though it may have effects beyond those borders. The court held that states can levy taxes on activities conducted wholly within their territory even when these activities are part of larger interstate transactions.

In the dissenting opinion for Western Union Telegraph Co. v. Pennsylvania, Justice Harlan argued that the majority's decision to strike down a Pennsylvania tax on interstate telegraph messages was incorrect and inconsistent with previous rulings of the Court. He contended that this tax did not discriminate against interstate commerce as it applied equally to both intrastate and interstate telegrams sent from within Pennsylvania. Furthermore, he pointed out that similar taxes had been upheld in other cases where they were imposed on gross receipts derived from both intra- and inter-state business activities conducted within a state’s borders. Therefore, according to him, there was no valid reason why such a tax should be considered unconstitutional when levied upon an entity like Western Union which operates extensively across state lines but also conducts significant business operations within individual states.