Failure to file tax returns may be either a felony or a misdemeanor pursuant to 26 U.S.C. § 7203, which states:

Any person required under this title to pay any estimated tax or tax, or required by this title or by regulations made under authority thereof to make a return, keep any records, or supply any information, who willfully fails to pay such estimated tax or tax, make such return, keep such records, or supply such information, at the time or times required by law or regulations, shall, in addition to other penalties provided by law, be guilty of a misdemeanor and, upon conviction thereof, shall be fined not more than $25,000 ($100,000 in the case of a corporation), or imprisoned not more than 1 year, or both, together with the costs of prosecution. In the case of any person with respect to whom there is a failure to pay any estimated tax, this section shall not apply to such person with respect to such failure if there is no addition to tax under section 6654 or 6655 with respect to such failure. In the case of a willful violation of any provision of section 6050I, the first sentence of this section shall be applied by substituting “felony” for “misdemeanor” and “5 years” for “1 year”.

As the Code states, if the failure to a file tax return is “willful” then the crime is elevated to a felony from a misdemeanor.  To prove that a defendant’s conduct was willful, the United States Supreme Court held that the prosecution must show three things: first, the law imposed a duty on the defendant; second, the defendant knew that he or she had a duty; and third, the defendant intentionally and voluntarily violated that duty. Cheek v. United States, 498 U.S. 192, 201 (1990).