Pillsbury Co. v. Conboy
In Pillsbury Co. v. Conboy (1983) 459 U.S. 248, a deponent in a civil case was held in contempt for refusing to answer questions that closely tracked questions he had already answered under a grant of federal statutory immunity.
In addition to noting that federal courts lack the power to confer immunity other than as authorized by statute, the court rejected the idea that a trial court could or should base such a ruling on forecasting the determination to be made in a later criminal trial. (Id. at p. 261.)
In holding the deponent in contempt, the trial court had "essentially predicted that a court in a future criminal prosecution ... would be obligated to protect against evidentiary use of the deposition testimony petitioners seek. We do not think such a predictive judgment is enough." (Ibid.)
Arguments to the contrary "imposed risks on the deponent whether or not the deposition testimony properly can be used against him in a subsequent criminal prosecution." (Id. at p. 262.)
The trial court's order of compulsion could not be "justified by the subsequent exclusion of the compelled testimony." (Ibid.)