In a motion to quash a grand jury subpoena issued against a defendant in a civil case, what are the grounds for the order to be quashed?

Appellants further argue that the subpoenas should be quashed because they are overbroad and unreasonable, lack specificity, and are not relevant to a criminal investigation. In this circuit we abide by the standard that "a court may not exercise its 'supervisory power' in a way which encroaches on the prerogatives of the [prosecutor and grand jury] unless there is a clear basis in fact and law for doing so. " United States v. Chanen, 549 F.2d 1306, 1313 (9th Cir.) (emphasis added), cert. denied, 434 U.S. 825 (1977). While appellants assert in their brief that production of the subpoenaed documents is unreasonably oppressive or that the subpoenas improperly advance a civil suit rather than a criminal investigation, appellants made no factual showing whatsoever of these or any other assertions before the district court. Neither the district court nor this court, of course, may accept appellants' counsel's bare assertions in place of the "clear basis in fact" that judicial exercise of supervisory control requires. Absent the required "clear basis in fact," appellants have not shown that the subpoenas are overbroad, unreasonable, oppressive, or irrelevant to the criminal investigation.