The U.S. Supreme Court case Buck v. Kuykendall in 1924 revolved around the issue of whether a state could regulate interstate commerce by requiring bus operators to obtain a certificate of convenience and necessity before operating within the state's borders. The plaintiff, Mr. Buck, was denied such a certificate by Mr. Kuykendall, Director of Public Works for Washington State, which prevented him from running his bus service between Spokane and Seattle despite having federal authorization to do so. The court ruled in favor of Buck on grounds that this requirement imposed an undue burden on interstate commerce and thus violated the Commerce Clause (Article I Section 8) of the Constitution which grants Congress exclusive power over it. This landmark decision established that states cannot interfere with or place restrictions upon businesses engaged in interstate commerce unless they can demonstrate that their regulations serve a legitimate public interest without unduly interfering with commercial activities across state lines.

In the dissenting opinion for Buck v. Kuykendall, Justice McReynolds argued that states should have the right to regulate their own commerce as they see fit. He believed that Washington state's law requiring a certificate of public convenience and necessity before operating a motor vehicle carrier business was not an unreasonable regulation or burden on interstate commerce. Instead, he saw it as a necessary measure to prevent wasteful competition and protect local businesses from being overwhelmed by larger out-of-state companies. He also pointed out that similar laws had been upheld in other cases involving railroads and utilities, so there was precedent for this type of regulation. In his view, striking down the law would undermine states' rights and potentially lead to unregulated competition causing harm to both businesses and consumers.