Two USSC rulings that might assist you in answering this

Posted on: May 21, 2019 at 15:40:59 CT

Congressional rules empower all its standing committees with the authority to compel witnesses to produce testimony and documents for subjects under its jurisdiction. Committee rules may provide for the full committee to issue a subpoena, or permit subcommittees or the chairman (acting alone or with the ranking member) to issue subpoenas.

As announced in Wilkinson v. United States,[7] a Congressional committee must meet
three requirements for its subpoenas to be "legally sufficient." First, the committee's investigation of the broad subject area must be authorized by its chamber; second, the investigation must pursue "a valid legislative purpose" but does not need to involve legislation and does not need to specify the ultimate intent of Congress; and third, the specific inquiries must be pertinent to the subject matter area that has been authorized for investigation.

The Court held in Eastland v. United States Servicemen's Fund[8] that Congressional subpoenas are within the scope of the Speech and Debate clause which provides "an absolute bar to judicial interference" once it is determined that Members are acting within the "legitimate legislative sphere" with such compulsory process. Under that ruling, courts generally do not hear motions to quash Congressional subpoenas; even when executive branch officials refuse to comply, courts tend to rule that such matters are "political questions" unsuitable for judicial remedy. In fact, many legal rights usually associated with a judicial subpoena do not apply to a Congressional subpoena. For example, attorney-client privilege and information that is normally protected under the Trade Secrets Act do not need to be recognized.[9]