Ex parte Milwaukee & Minnesota Railroad Co. was a United States Supreme Court case that dealt with the issue of whether a state court had the authority to issue an injunction against a railroad company. The case arose when the Minnesota Supreme Court issued an injunction against the Milwaukee & Minnesota Railroad Company, ordering it to cease operations in the state. The railroad company argued that the injunction was unconstitutional because it violated the Commerce Clause of the United States Constitution, which gives Congress the power to regulate interstate commerce. The Supreme Court held that the injunction was unconstitutional because it interfered with interstate commerce. The Court reasoned that the Commerce Clause gave Congress the exclusive power to regulate interstate commerce, and that the state court did not have the authority to issue an injunction that would interfere with interstate commerce. The Court also held that the injunction was an unconstitutional violation of the railroad company's right to due process of law. The Court's decision in Ex parte Milwaukee & Minnesota Railroad Co. established the principle that state courts cannot issue injunctions that interfere with interstate commerce. This decision has been cited in numerous cases since then, and it remains an important precedent in the area of interstate commerce.

In the dissenting opinion of Ex Parte Milwaukee & Minnesota Railroad Co., Justice Field argued that Congress had not intended to grant the power sought by the petitioners. He noted that while Congress had granted certain powers to railroads, it did not include any authority for them to take private property without just compensation. Furthermore, he stated that even if such a power was implied in some way from other legislation, it would still be unconstitutional as taking private property without due process of law is prohibited by both state and federal constitutions. In conclusion, Justice Field argued that granting this type of power would amount to an unconstitutional exercise of legislative authority and should therefore be denied.