In Packet Company v. St. Louis, the Supreme Court of the United States was asked to decide whether a city ordinance that prohibited steamboats from docking at the city's wharves was constitutional. The Packet Company, a steamboat company, argued that the ordinance violated the Commerce Clause of the United States Constitution, which gives Congress the power to regulate interstate commerce. The Supreme Court held that the ordinance was unconstitutional. The Court reasoned that the ordinance was an attempt to regulate interstate commerce, which is a power reserved for Congress. The Court noted that the ordinance would have a direct effect on interstate commerce, as it would prevent steamboats from docking at the city's wharves and thus impede the flow of goods and services between states. The Court also held that the ordinance was an unconstitutional exercise of the city's police power. The Court reasoned that the ordinance was not necessary to protect the public health, safety, or welfare, and thus was an improper exercise of the city's police power. In conclusion, the Supreme Court held that the ordinance was unconstitutional and could not be enforced.

Justice Field delivered the dissenting opinion in Packet Company v. St. Louis, arguing that the majority's decision was incorrect and should be reversed. He argued that under Missouri law, a municipality had no power to impose taxes on vessels or their owners for using its waters as a highway of commerce unless authorized by an act of Congress or by some contract between the parties. The City of St. Louis had imposed such a tax on steamboats owned by Packet Company without any authorization from either Congress or any agreement with them, which Justice Field deemed illegal and unconstitutional because it violated both state and federal laws protecting interstate commerce from taxation without consent from Congress first being obtained. Furthermore, he argued that even if there were some sort of implied authority granted to municipalities to levy taxes upon vessels navigating within their limits, this did not extend beyond what was necessary for local purposes; since the tax imposed here exceeded those needs it could not be justified as validly enacted under municipal authority alone but must have been done so with Congressional approval first having been sought out - something which had clearly not happened in this case according to Justice Field's interpretation of events leading up to it being brought before court