A grand jury was convened to investigate possible violations of federal criminal statutes relating to gambling. The grand jury subpoenaed Dioinisio (D) and 19 others to give a voice exemplar in order to compare them with prior recorded conversations. D refused. The United States (P) then filed petitions to compel D and the other witnesses to furnish the voice exemplars to the grand jury. The District Judge rejected the constitutional arguments and ordered Ds to comply with the grand jury's request. D persisted in his refusal to respond. The District Court adjudged him in civil contempt and ordered him committed to custody until he obeyed the court order, or until the expiration of 18 months. The Court of Appeals reversed: To compel the voice recordings would violate the Fourth Amendment. The court found that the Fourth Amendment applied to grand jury process, and that, 'under the fourth amendment, law enforcement officials may not compel the production of physical evidence absent a showing of the reasonableness of the seizure. The Supreme Court granted certiorari.

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