The U.S. Supreme Court case Michael Hartman et al. v. William G. Moore, Jr., 2005 revolved around the issue of retaliatory prosecution in violation of First Amendment rights and whether probable cause can be used as a defense by federal officials against such claims. The plaintiff, William G. Moore Jr., was a former president of an express mail company who alleged that he was prosecuted for bribery because he had publicly criticized the United States Postal Service (USPS). He claimed this retaliation violated his First Amendment rights and sued five USPS investigators under Bivens v Six Unknown Named Agents precedent which allows individuals to sue federal officers for constitutional violations. The court ruled in favor of the defendants stating that if there is probable cause to support an underlying criminal charge then it defeats a claim of retaliatory prosecution even if animus is proven - unless it can be shown that but-for the retaliatory motive, legal proceedings would not have commenced.

In the dissenting opinion for Hartman v. Moore, Justice Breyer argued that a plaintiff should not have to prove an absence of probable cause in order to establish retaliatory prosecution. He believed this requirement was unnecessary and could potentially deter victims of retaliation from seeking justice due to the difficulty in proving such a negative. Furthermore, he pointed out that there are already safeguards in place within the legal system - including prosecutorial discretion and judicial review - which can prevent frivolous lawsuits based on claims of retaliation. Therefore, adding another layer of proof would only serve as an additional barrier for plaintiffs without significantly improving the quality or legitimacy of cases brought before courts.