In the case of Federal Trade Commission v. Simplicity Pattern Co., Inc., the Supreme Court ruled in favor of the Federal Trade Commission (FTC). The FTC had accused Simplicity Pattern Co. of engaging in unfair methods of competition by selling its products at a lower price to some customers than others, violating Section 2(a) of the Clayton Act as amended by Robinson-Patman Act. The company defended itself arguing that it was entitled to meet an equally low price offered by a competitor under section 2(b) defense and claimed that FTC failed to prove injury to competition which is required for establishing violation under section 2(a). However, Supreme Court rejected these arguments stating that there was substantial evidence supporting FTC's findings and held that proof of competitive injury can be inferred from practices like systematic discriminatory pricing over time.

In the dissenting opinion for the Federal Trade Commission v. Simplicity Pattern Co., Inc., it was argued that there was no substantial evidence to support the majority's conclusion that Simplicity had monopolized or attempted to monopolize any part of trade or commerce. The dissent pointed out that while Simplicity did have a large market share, this alone does not constitute monopoly power if other competitors are still able to operate effectively in the marketplace. Furthermore, they contended that there were no barriers preventing new companies from entering into competition with Simplicity and thus, its dominant position could be challenged at any time. They also disagreed with the majority's finding of predatory practices by pointing out these practices were common business strategies used by many firms and did not necessarily indicate an attempt to create a monopoly. Therefore, they believed that FTC failed in proving their case against Simplicity.