39 USC 3202 - Penalty mail

(a) Subject to the limitations imposed by sections 3204 and 3207 of this title, there may be transmitted as penalty mail
(1) official mail of
(A) officers of the Government of the United States other than Members of Congress;
(B) the Smithsonian Institution;

view counter
(C) the Pan American Union;
(D) the Pan American Sanitary Bureau;
(E) the United States Employment Service and the system of employment offices operated by it in conformity with the provisions of sections 49–49c, 49d, 49e–49k of title 29, and all State employment systems which receive funds appropriated under authority of those sections; and
(F) any college officer or other person connected with the extension department of the college as the Secretary of Agriculture may designate to the Postal Service to the extent that the official mail consists of correspondence, bulletins, and reports for the furtherance of the purpose of sections 341–343 and 344–348 of title 7;
(2) mail relating to naturalization to be sent to the Immigration and Naturalization Service by clerks of courts addressed to the Department of Justice or the Immigration and Naturalization Service, or any official thereof;
(3) mail relating to a collection of statistics, survey, or census authorized by title 13 and addressed to the Department of Commerce or a bureau or agency thereof; and
(4) mail of State agriculture experiment stations pursuant to sections 325 and 361f of title 7.
(b) A department or officer authorized to use penalty covers may enclose them with return address to any person from or through whom official information is desired. The penalty cover may be used only to transmit the official information and endorsements relating thereto.
(c) This section does not apply to officers who receive a fixed allowance as compensation for their services including expenses of postage.