From the CRS report, Obstruction of Congress: A Brief Overview of Federal Law Relating to Interference with Congressional Activities (Nov. 5, 2010 RL34304):
Obstruction of justice is the frustration of governmental purposes by violence, corruption, destruction of evidence, or deceit. It is a federal crime. In fact, federal obstruction of justice laws are legion; too many for even passing reference to all of them in a single report. This is a brief description of those that outlaw interference with congressional activities.
See also Bradley J. Bondi, No Secrets Allowed: Congress’s Treatment and Mistreatment of the Attorney-Client Privilege and the Work-Product Protection in Congressional Investigations and Contempt Proceedings, 25 Journal of Law and Politics, No. 145 (2010)(“To the extent Congress refuses to accept a witness’s assertion of the attorney-client privilege or work-product protection during an investigation, this article explores avenues for challenging such an adverse determination and for resisting the disclosure of the confidential information in the face of contempt. The article concludes with a discussion of some practical ways an individual or entity subject to a congressional investigation may limit the extent of any subsequent waiver and minimize the harm caused by the release of the information.”) — Joe