In the case of Cincinnati Soap Co. v. United States in 1936, the Supreme Court ruled on a matter related to antitrust laws and unfair competition practices. The Cincinnati Soap Company was accused by the government of violating Section 3 of the Clayton Act, which prohibits certain exclusive dealing arrangements that may lessen competition or create a monopoly. Specifically, they were alleged to have entered into contracts with retailers that required them to exclusively sell their soap products for a specified period in exchange for advertising allowances and other benefits. The court held that such agreements did not necessarily violate antitrust laws if they didn't substantially lessen competition or tend towards monopoly within any line of commerce where its effect might be substantial. It found no evidence showing these contracts had an adverse impact on competitors nor did it establish monopolistic control over soap sales by Cincinnati Soap Co., hence ruling in favor of the company. This decision clarified how courts should interpret and apply Section 3 of Clayton Act regarding exclusive dealing arrangements - focusing more on whether such deals actually harm market competitiveness rather than merely their existence.

In the dissenting opinion for Cincinnati Soap Co. v. United States, the justice argued that the majority's decision to uphold a tax on imported vegetable oils used in soap manufacturing was incorrect and inconsistent with previous rulings of the court. The dissent focused on two main points: first, it contended that this tax was not an excise but rather a duty or impost which is constitutionally required to be uniform throughout all states; secondly, it claimed that even if considered as an excise tax, there were no grounds for its imposition since these oils are raw materials and not manufactured products. Furthermore, they pointed out inconsistencies between this ruling and prior decisions involving similar circumstances where taxes were struck down because they violated constitutional principles of uniformity or because they constituted direct taxation without apportionment among states according to population.