26 U.S. Code § 7213 - Unauthorized disclosure of information (in part)
(a) Returns and return information
(1) Federal employees and other persons
It shall be unlawful for any officer or employee of the United States or any person described in section 6103
(or an officer or employee of any such person), or any former officer or employee, willfully to disclose to any person, except as authorized in this title, any return or return information (as defined in section 6103(b)). Any violation of this paragraph shall be a felony punishable upon conviction by a fine in any amount not exceeding $5,000, or imprisonment of not more than 5 years, or both, together with the costs of prosecution, and if such offense is committed by any officer or employee of the United States, he shall, in addition to any other punishment, be dismissed from office or discharged from employment upon conviction for such offense.
(2) State and other employees
It shall be unlawful for any person (not described in paragraph (1)) willfully to disclose to any person, except as authorized in this title, any return or return information (as defined in section 6103(b)) acquired by him or another person under subsection (d), (i)(1)(C), (3)(B)(i), or (7)(A)(ii), (k)(10), (l)(6), (7), (8), (9), (10), (12), (15), (16), (19), (20), or (21) or (m)(2), (4), (5), (6), or (7) of section 6103 or under section 6104(c). Any violation of this paragraph shall be a felony punishable by a fine in any amount not exceeding $5,000, or imprisonment of not more than 5 years, or both, together with the costs of prosecution.
And this part would cover the stupid Rachel Maddow
(3) Other persons
It shall be unlawful for any person to whom any return or return information (as defined in section 6103(b)) is disclosed in a manner unauthorized by this title thereafter willfully to print or publish in any manner not provided by law any such return or return information. Any violation of this paragraph shall be a felony punishable by a fine in any amount not exceeding $5,000, or imprisonment of not more than 5 years, or both, together with the costs of prosecution.