In the United States v. Portal case of 1914, the Supreme Court addressed a dispute involving import duties on goods from Puerto Rico to mainland U.S. The plaintiff, Portal, argued that as per the Foraker Act of 1900 (which established civil government in Puerto Rico after its acquisition by the U.S.), goods transported between Puerto Rico and mainland U.S should not be subject to customs duties. However, this was contradicted by an act passed in 1909 which imposed such taxes. The court ruled against Portal stating that Congress had full authority over territories like Puerto Rico and could impose tariffs if it deemed necessary for public policy reasons or revenue generation purposes. Therefore, despite being part of US territory, trade with Puerto Rico could still be subjected to taxation under federal law.

The dissenting opinion in the United States v. Portal case of 1914 argued that the majority's decision to convict Mr. Portal was incorrect because it failed to consider his intent when he committed the act for which he was charged. The dissenting justices believed that, while Mr. Portal did indeed commit an illegal act, there was no evidence presented during trial indicating that he intended to defraud anyone or gain any personal benefit from his actions; rather, they suggested that all indications pointed towards him acting out of ignorance and misunderstanding about what constituted legal behavior under U.S law at the time. They further contended that this lack of malicious intent should have been a significant factor in determining whether or not Mr. Portal deserved punishment for his actions.