In United States v. De Haro, the Supreme Court considered whether a Mexican citizen who had been living in California since 1848 was entitled to protection under the Treaty of Guadalupe Hidalgo. The treaty provided that Mexicans residing in territories ceded by Mexico to the United States would be allowed to remain and enjoy all rights of citizens of the US, including property rights. The court held that De Haro was indeed protected by this treaty and thus his land could not be taken away from him without due process as required by law. This decision established an important precedent for protecting immigrants' property rights regardless of their citizenship status or place of origin.

In United States v. De Haro, the Supreme Court was asked to decide whether a Mexican citizen who had been living in California since before it became part of the United States could be considered an American citizen and thus eligible for protection under U.S. law. The majority opinion held that he could not because he did not meet the requirements set forth by Congress in order to become a naturalized citizen of the United States at that time; however, Justice Field dissented from this ruling on two grounds: first, that there was no evidence presented which showed that De Haro had ever renounced his allegiance to Mexico or declared himself as an American citizen; second, even if such evidence existed, Congress lacked authority to pass laws concerning citizenship without approval from both houses of Congress and ratification by three-fourths of all states—a requirement which had never been met in this case. In conclusion, Justice Field argued that denying De Haro's claim would violate due process rights guaranteed under the Fifth Amendment and should therefore be overturned.