Ex parte: In the Matter of the United States is a landmark Supreme Court case that established the power of the federal government to enforce the Reconstruction Amendments. The case arose from a dispute between the United States and the state of Mississippi over the enforcement of the Fourteenth Amendment. The state of Mississippi had passed a law that prohibited African Americans from voting in state elections. The United States argued that this law violated the Fourteenth Amendment, which guarantees all citizens equal protection under the law. The Supreme Court agreed, ruling that the federal government had the power to enforce the Reconstruction Amendments and that the state of Mississippi had violated the Fourteenth Amendment. This ruling established the federal government's power to enforce the Reconstruction Amendments and was a major victory for civil rights.

In Ex Parte: In the Matter of the United States, a dissenting opinion was issued by Justice Field. He argued that Congress had no authority to pass legislation which would allow for the suspension of habeas corpus during times of rebellion or insurrection. He noted that this power was reserved solely for the President under Article I, Section 9, Clause 2 of the Constitution and could not be delegated to another branch. Furthermore, he argued that even if Congress did have such authority it should only be used in extreme circumstances and not as a means to suppress political dissent or opposition. Finally, he asserted that any laws passed by Congress must comply with due process requirements set forth in both state and federal constitutions before they can be enforced against individuals accused of crimes or offenses against them.