From the Congressional Research Service's 'Congressional Oversight Manual' :
http://www.fas.org/sgp/crs/misc/RL30240.pdfCongress recognized the problem raised by its inability to punish a contemnor
beyond the adjournment of a congressional session. In 1857, Congress enacted a
statutory criminal contempt procedure as an alternative to the inherent contempt
procedure that, with minor amendments, is codified today at 2 U.S.C. §§192 and 194.
A person who has been subpoenaed to testify or produce documents before the House or Senate or a committee and who fails to do so, or who appears but refuses to respond to questions, is guilty of a misdemeanor, punishable by a fine of up to $100,000 and imprisonment for up to one year.
A contempt citation must be approved by the subcommittee, the full committee, and the full House or Senate (or by the presiding officer if Congress is not in session). After a contempt has been certified by the President of the Senate or the Speaker of the House, it is the “duty” of the U.S. Attorney “to bring the matter before the grand jury for its action.”The criminal contempt procedure was rarely used until the twentieth century, but since 1935 it has been essentially the exclusive vehicle for punishment of contemptuous conduct. Prior to Watergate, no executive branch official had ever been the target of a criminal contempt proceeding. Since 1975, however, 10 cabinet-level or senior executive officials have been cited for contempt for failure to produce subpoenaed documents by either a subcommittee, a full committee, or by a House.
In each instance there was substantial or full compliance with the document demands before the initiation of criminal proceedings. However, following the vote of contempt of EPA Administrator Anne Gorsuch Burford, but before the contempt citation was forwarded to the United States Attorney for grand jury action, the Department of Justice raised the question whether Congress could compel the U.S. Attorney to submit the citation for grand jury consideration.
The documents in question were turned over to Congress before the issue was litigated in court.
The question of the duty of the U.S. Attorney under section 192 to enforce contempt of Congress citations remains unresolved and has left some uncertainty as to the efficacy of the use of criminal contempt proceedings against executive branch officials.http://www.fas.org/sgp/crs/misc/RL30240.pdfThe White House attempted to define the "duty" of the U.S. Attorney to refer the citation to a grand jury by claiming their own Justice Dept.'s assertion of 'executive privilege' would prevent the office from acting.
However, Subcommittee Chairwoman Linda Sánchez replied that White House claims of executive privilege cannot be used as a blanket protection to avoid congressional oversight as authorized by the Constitution. And that, White House assertions do not release the subjects of the subpoenas from their obligation to comply.