In the case of Federal Trade Commission v. R.F. Keppel & Bro., Inc., 1933, the U.S Supreme Court ruled in favor of the Federal Trade Commission (FTC). The FTC had accused R.F Keppel & Bro., a candy manufacturer, of unfair competition by selling its products at lower prices to large buyers than to small ones, which was considered as price discrimination under Section 5 of the Federal Trade Commission Act. The court held that such practices were detrimental to commerce and violated federal law even if they did not harm individual competitors directly but affected overall market conditions negatively. This decision reinforced that any business practice affecting commerce adversely could be deemed unlawful under this act regardless of whether it involved interstate trade or not.

In the dissenting opinion for Federal Trade Commission v. R.F. Keppel & Bro., Inc., Justice McReynolds disagreed with the majority's interpretation of "unfair methods of competition." He argued that it was not within the purview of the FTC to determine what constitutes an unfair method, especially in cases where no clear harm or deception is present. The justice believed that this broad interpretation could lead to arbitrary and unpredictable enforcement by the commission, potentially stifling legitimate business practices. Furthermore, he contended that such a wide-ranging authority should be explicitly granted by Congress rather than inferred from ambiguous language in legislation.