The U.S. Supreme Court case Postal Telegraph-Cable Co. v. Taylor in 1903 revolved around the interpretation of a contract between the plaintiff, Postal Telegraph-Cable Company, and the defendant, Mr. Taylor who was an agent for another telegraph company at that time when he entered into this agreement with the plaintiff's predecessor firm (Western Union). The dispute arose over whether or not Mr.Taylor had breached his contractual obligations by failing to forward all messages received from other lines to Western Union exclusively as per their agreement which also included a clause prohibiting him from acting as an agent for any other telegraph company during its term. The court ruled in favor of Mr.Taylor stating that while it is true that he did agree not to act as an agent for any other company during his tenure with Western Union, there was no explicit provision within their contract stipulating that he must forward all incoming messages solely through them; thus making him free to transmit these via whichever line seemed most expedient without breaching said contract.

In the dissenting opinion for Postal Telegraph-Cable Co. v. Taylor, Justice Harlan argued that the majority's decision was a misinterpretation of both state and federal law. He contended that it was not within the power of Congress to regulate intrastate commerce, which he believed this case fell under due to its nature as a contract dispute between private parties in one state. Furthermore, he disagreed with the majority's assertion that telegraph companies were agents or instrumentalities of interstate commerce simply because they transmitted messages across state lines; instead, he viewed them as independent entities operating under their own contracts and regulations within each individual state where they conducted business.