In the case of Salt Company v. East Saginaw, the Supreme Court of the United States was asked to decide whether a state law that imposed a tax on salt was constitutional. The Salt Company argued that the law violated the Commerce Clause of the Constitution, which gives Congress the power to regulate interstate commerce. The Court held that the law was constitutional, as it did not interfere with interstate commerce. The Court reasoned that the law was a valid exercise of the state's power to tax, and that it did not discriminate against interstate commerce. The Court also noted that the tax was not excessive, and that it was applied uniformly to all salt producers in the state. The Court's decision in this case established the principle that states may impose taxes on goods that are produced within their borders, even if those goods are sold in other states. This decision has been cited in numerous subsequent cases, and it remains an important precedent in the area of state taxation.

In the case of Salt Company v. East Saginaw, Justice Field delivered a dissenting opinion in which he argued that the majority's decision was contrary to both precedent and sound legal reasoning. He asserted that it was not within the power of a state legislature to grant exclusive privileges or immunities to any corporation, as this would be an unconstitutional interference with private rights. Furthermore, he argued that even if such powers were granted by statute, they could only be exercised for public purposes and not for private gain; thus, granting exclusive salt-making privileges solely to one company violated this principle. Additionally, Field maintained that since no contract existed between East Saginaw and Salt Company prior to their agreement on these terms—and because there had been no consideration given by either party—the agreement should have been declared void ab initio (from its inception). Finally, Field concluded his dissent by noting that while states may pass laws regulating trade or commerce within their borders so long as those laws do not conflict with federal law or interfere with individual rights protected under the Constitution; however in this case neither condition applied making it clear why he disagreed with the Court’s ruling.