In Beatty v. The State of Maryland, the Supreme Court ruled that a state law which imposed a tax on all vessels entering its ports was unconstitutional as it violated the Supremacy Clause of the Constitution. This case arose when Captain John Beatty refused to pay taxes for his vessel upon entering Baltimore harbor in 1810 and was subsequently arrested by local authorities. He then filed suit against Maryland claiming that their taxation laws were invalid under federal law because they interfered with Congress’s power to regulate commerce among states and foreign nations. In an opinion written by Chief Justice Marshall, the court held that while states had some authority over matters within their borders, this did not extend to taxing vessels from other jurisdictions or regulating interstate trade without congressional approval; thus, Maryland's tax on ships was found unconstitutional as it infringed upon Congress' exclusive right to regulate commerce between states and foreign countries.

In Beatty v. The State of Maryland, Chief Justice Marshall delivered a dissenting opinion on behalf of himself and two other justices. He argued that the state had no right to impose an additional tax on goods imported from another state because it was unconstitutional under the Commerce Clause of the Constitution. According to Marshall, this clause gave Congress exclusive power over interstate commerce and prohibited states from interfering with or regulating it in any way. Furthermore, he asserted that if a state were allowed to levy taxes on imports from other states then they would be able to control trade between them which is something only Congress has authority over according to Article I Section 8 of the Constitution. Therefore, he concluded that such taxation by Maryland was unconstitutional and should not have been upheld by majority decision as it violated federal law established by Congress through their constitutional powers granted in Article I Section 8.