The Pennsylvania Railroad Company v. Public Service Commission of the Commonwealth of Pennsylvania case in 1919 revolved around a dispute between the railroad company and the state's public service commission over rates for intrastate freight transportation. The Supreme Court was tasked with determining whether or not it was within the power of a state to regulate these rates, even if they were lower than those set by federal law for interstate commerce. In its decision, the court held that states do have this authority as long as their actions don't interfere with interstate commerce regulations established by Congress under its Commerce Clause powers. However, in this specific instance, it found that Pennsylvania's rate-setting did indeed conflict with federal regulation and thus violated the Supremacy Clause of U.S Constitution which establishes Federal law as supreme over State laws when there is a conflict between them.

In the dissenting opinion for Pennsylvania Railroad Company v. Public Service Commission of the Commonwealth of Pennsylvania, Justice McReynolds disagreed with the majority's ruling that a state could regulate intrastate railroad rates even when they affected interstate commerce. He argued that this decision was inconsistent with previous rulings and would lead to confusion in future cases. He believed it was not within a state's power to control or influence interstate commerce through its regulation of intrastate activities, as such actions should be under federal jurisdiction according to the Commerce Clause in U.S Constitution. Furthermore, he expressed concern about potential negative impacts on businesses due to varying regulations across different states if each were allowed to set their own rules without any overarching federal guidance or consistency.