The United States Postal Service v. Flamingo Industries (USA) Ltd., et al., 2003, is a case that revolved around whether the U.S. Postal Service could be considered a "person" under the Sherman Antitrust Act and thus subject to its provisions. The dispute began when Flamingo Industries alleged that the USPS had violated antitrust laws by monopolizing mail transportation and delivery services after it stopped purchasing mail sacks from them in favor of producing these items internally. However, the Supreme Court ruled unanimously in favor of USPS, stating that it was not a "person" as defined by antitrust law due to its status as an independent establishment of the executive branch of government with substantial governmental powers and duties. Therefore, it was exempted from liability under such laws.

In the dissenting opinion for United States Postal Service v. Flamingo Industries (USA) Ltd., Justice Breyer argued that the majority's decision to treat the U.S. Postal Service as a government agency, rather than a commercial enterprise, was incorrect and inconsistent with precedent. He pointed out that Congress had specifically designed the USPS to be self-supporting and competitive in commercial markets, which distinguished it from typical federal agencies. Therefore, he believed it should not enjoy immunity from antitrust laws like other governmental entities do under sovereign immunity doctrine. Moreover, he noted that this ruling could have far-reaching implications by potentially extending similar immunities to other government corporations operating in commercial arenas.