In the case of United States v. Caceres, the U.S. Supreme Court ruled in favor of the government, stating that evidence obtained by Internal Revenue Service (IRS) agents through unauthorized electronic surveillance could be used against a taxpayer in court. The defendant, Manuel Caceres, had been convicted for offering bribes to an IRS agent based on recordings made during their meetings without his knowledge or consent. He appealed his conviction arguing that these recordings were made contrary to IRS regulations and should not have been admitted as evidence at trial because they violated his Fourth Amendment rights against unreasonable searches and seizures. The Supreme Court disagreed with this argument saying that while it was true that the recording did violate internal IRS rules regarding electronic surveillance; those rules did not confer any constitutional rights upon taxpayers nor create any legally enforceable expectations of privacy beyond what is provided under existing law. Therefore, even though there was a violation of internal procedures within the agency itself when obtaining this evidence - it did not amount to a constitutional violation which would require suppression of said evidence.

In the dissenting opinion for United States v. Caceres, Justice Brennan disagreed with the majority's decision to exclude evidence on procedural grounds. He argued that excluding evidence because of a failure to comply with internal IRS regulations was not appropriate or necessary under the Fourth Amendment, which protects against unreasonable searches and seizures. Instead, he believed that such issues should be addressed through administrative channels rather than by suppressing potentially crucial evidence in criminal proceedings. Furthermore, he expressed concern about how this ruling could impact future cases where government agencies fail to follow their own procedures - suggesting it might encourage defendants to focus on technicalities rather than substantive legal issues.