In the United States v. Powell case of 1984, the Supreme Court ruled in favor of the government's right to issue a summons for tax investigation purposes without having to show probable cause that a tax law violation had occurred. The Internal Revenue Service (IRS) issued several summonses to Powell and his wife as part of an investigation into their potential income underreporting. When they refused, citing lack of probable cause, the IRS sought enforcement through district court which was granted but later reversed by an appellate court on grounds that there must be some preliminary showing indicating fraud before such summonses could be enforced. However, upon reaching Supreme Court level it was decided that no such requirement existed within existing laws or constitutionally; therefore reversing again in favor of IRS' original position.

In the dissenting opinion for United States v. Powell, Justice Brennan disagreed with the majority's interpretation of 18 U.S.C. § 6002 and its application to this case. He argued that the statute should be read in a way that protects individuals from being prosecuted based on evidence derived directly or indirectly from their immunized testimony, which he believed was not done in this case. According to him, any information obtained through such testimony should not be used as an "investigatory lead" or a source of legitimate evidence against them unless it can be proven beyond reasonable doubt that it would have been discovered without using their compelled testimonies as starting point. In his view, allowing otherwise would undermine Fifth Amendment protections against self-incrimination and violate principles of fundamental fairness enshrined in due process clause.