In the case of Pillsbury Co. et al. v. Conboy, 1982, the United States Supreme Court ruled that a witness who testifies under grant of immunity cannot be compelled to sign a waiver allowing his testimony to be used against him in foreign prosecutions. The case arose when Kevin P. Mulcahy was subpoenaed by a grand jury investigating alleged price-fixing in the heavy electrical equipment industry and refused to testify unless granted immunity from prosecution based on any information he provided or derived therefrom (transactional immunity). After being granted use and derivative-use immunity instead, which only protected him from domestic prosecution using his testimony or evidence derived from it but not independent evidence, Mulcahy testified before another grand jury about possible antitrust violations involving foreign companies and governments but refused to sign waivers permitting such foreign entities to use his testimony against him fearing potential criminal liability abroad for activities within their jurisdiction.

In the dissenting opinion for Pillsbury Co. et al. v. Conboy, Justice William Rehnquist disagreed with the majority's interpretation of Rule 26(b)(3) of the Federal Rules of Civil Procedure regarding work-product doctrine and its application to a former employee’s memory about information learned during employment. He argued that such an expansive reading could potentially shield any information from discovery merely because it was once noted by an attorney, which he believed contradicted previous court rulings and legislative intent behind this rule. Furthermore, he contended that treating memories as discoverable documents would place undue burdens on litigation processes due to difficulties in determining when a memory becomes protected work product or not.