In the Armstrong Paint & Varnish Works v. Nu-Enamel Corp case of 1938, the Supreme Court ruled on a matter concerning unfair competition and trademark infringement. The plaintiff, Armstrong Paint & Varnish Works, accused Nu-Enamel Corporation of using deceptive practices to sell their product as if it were that of Armstrong's. They alleged that this was causing confusion among customers and damaging their business reputation. However, the court found in favor of Nu-Enamel Corporation stating there was no evidence proving any intent to deceive or cause confusion among consumers by selling similar products under different brand names with distinct labels and packaging designs. Furthermore, they stated that mere similarity between two products does not constitute an act of unfair competition unless there is clear proof showing intention to mislead buyers into thinking they are purchasing a different product than what is actually being sold.

In the dissenting opinion for Armstrong Paint & Varnish Works v. Nu-Enamel Corp., Justice Black disagreed with the majority's decision to uphold a lower court ruling that found Armstrong guilty of violating anti-trust laws by conspiring to fix prices and control distribution in violation of the Sherman Act. He argued that there was insufficient evidence presented at trial to prove such conspiracy, particularly given that no direct proof or explicit agreement among defendants was shown. Furthermore, he contended that mere parallel business behavior does not necessarily constitute an illegal act under antitrust law; it could simply be a result of similar reactions to identical market conditions. Thus, he believed this case should have been dismissed due its lack of substantial evidence proving conspiracy beyond reasonable doubt.