The United States v. National Dairy Products Corp. case in 1962 revolved around the Sherman Act, which prohibits certain business activities that federal government regulators deem to be anti-competitive. The U.S government accused National Dairy Products Corporation and its subsidiary, Breyer's Ice Cream Company of violating this act by purchasing milk from farmers at prices below those stipulated by Pennsylvania Milk Control Commission regulations. The defendants argued that their actions were not illegal because they were complying with state law and claimed immunity under the Parker Doctrine (which exempts states from federal antitrust laws). However, the Supreme Court ruled against them stating that a private party who violates antitrust laws cannot claim immunity based on compliance with state law unless it is compelled to do so by the state acting as a sovereign.

In the dissenting opinion for United States v. National Dairy Products Corp., Justice Harlan argued that the majority's interpretation of the Robinson-Patman Act was overly broad and inconsistent with its legislative history. He contended that Congress intended to prohibit only those price discriminations which have a reasonable possibility of harming competition, not all price differences between purchasers as such. The justice also criticized the majority's reliance on administrative interpretations, stating they were neither contemporaneous nor consistent enough to be given controlling weight in interpreting statutory language. Furthermore, he believed it was inappropriate for courts to defer so heavily to administrative agencies when interpreting criminal statutes because this could lead to arbitrary enforcement and undermine legal certainty necessary for fair warning in criminal law.