Technically they can, and have been since the 18th century. [More here.](https://www.law.cornell.edu/wex/contempt_of_congress) Snippet: > Currently, actions for which individuals can be held in contempt of Congress are largely a matter of statutory law and focus mostly on when individuals refuse to appear or give testimony for a Congressional investigation or hearing. The U.S. Supreme Court in Watkins v. United States confirmed Congressional power to issue subpoenas, stating that all citizens have a duty to “cooperate with the Congress in its efforts to obtain the facts needed for intelligent legislative action,” and that they must “respond to subpoenas [and] testify.” Federal law penalizes individuals who refuse to respond to Congressional inquiries, as 2 U.S.C. § 192 states that any person who is summoned before Congress who "willfully makes default, or who, having appeared, refuses to answer any question pertinent to the question under inquiry" shall be guilty of a misdemeanor, and may be subject to a fine and imprisonment if convicted. > The matter under Congressional investigation, however, must be a subject over which Congress has legislative power before an uncooperative witness may be convicted of contempt. The U.S. Supreme Court in Quinn v. United States also recognized certain limitations on Congressional power to investigate and summon individuals, namely, that it “cannot be used to inquire into private affairs unrelated to a valid legislative purpose. Nor does it extend to an area in which Congress is forbidden to legislate. Similarly, the power to investigate must not be confused with any of the powers of law enforcement; those powers are assigned under our Constitution to the Executive and the Judiciary. Still further limitations on the power to investigate are found in the specific individual guarantees of the Bill of Rights, such as the Fifth Amendment's privilege against self-incrimination which is in issue here.”