The US Congress, by right of a 1938 law has the right to require people to appear before either body (House or Senate). This is issued in the form of a subpoena in most cases. When a person fails to appear or fails to testify, Congress is empowered by the same law to find the person in contempt of congress. More loosely, any person who impedes a congressional investigation may be cited as being in contempt. Acts impeding an investigation include failing to appear when summoned, failing to produce requested documents, or lying to congress in an attempt to obstruct an investigation.
Contempt of congress is very much like being held in contempt by a judge or a federal or state court. If you fail to answer a subpoena in a regular court can earn you a contempt citation. Similarly refusing to answer questions if you do appear and are doing things like hiding evidence pertaining to an investigation, you can be charged with contempt.
Another similarity in contempt of congress is your rights if you receive a subpoena. Under most circumstances, you can claim 5th Amendment rights if testimony you give would be self-incriminating. If the House or Senate is investigating some scandal that directly concerns the person subpoenaed, the person need not incriminate himself by giving testimony. Still, failure to answer the subpoena and appear as appointed may have repercussions. It is in fact breaking a law.
Under current US law, a person found in contempt of congress has committed a misdemeanor, may serve up to 12 months in prison and may be fined. It is up to the house conducting the investigation to determine whether such fines or a prison sentence are appropriate. Sometimes Congress does not act even on cases where a person is in longstanding contempt. The hope may be that simply declaring someone in contempt of congress may result in his or her appearance, though this is not always the case.
When the term first evolved, contempt of congress was often defined as bribing a congressperson to act in a specific way, which was undoubtedly contemptuous, but this is no longer the case. Now it most often refers to an accusation by either of the houses that a person has failed to answer a summons to appear or a summons for documentation. There are some tests to subpoenas that can be made. For instance, a person can argue that Congress has insufficient evidence to warrant a subpoena.
There have been a number of people cited on contempt charges. In the last few decades, Janet Reno and Karl Rove were both held in contempt. One of the most well known cases in relatively recent times, that did result in an actual prison sentence was when the House of Representatives held the Environmental Protection Agency’s (EPA) Rita Lavelle in contempt for her testimony. She received six months in prison and was fined $10,000 US Dollars (USD) for lying during the House’s investigation of misuse of EPA funds.