42 U.S.C. § 1437i

(a) Obligations issued by a public housing agency in connection with low-income housing projects which (1) are secured (A) by a pledge of a loan under any agreement between such public housing agency and the Secretary, or (B) by a pledge of annual contributions under an annual contributions contract between such public housing agency and the Secretary, or (C) by a pledge of both annual contributions under an annual contributions contract and a loan under an agreement between such public housing agency and the Secretary, and (2) bear, or are accompanied by, a certificate of the Secretary that such obligations are so secured, shall be incontestable in the hands of a bearer and the full faith and credit of the United States is pledged to the payment of all amounts agreed to be paid by the Secretary as security for such obligations. (b) Except as provided in section 1437c(g) of this title , obligations, including interest thereon, issued by public housing agencies in connection with low-income housing projects shall be exempt from all taxation now or hereafter imposed by the United States whether paid by such agencies or by the Secretary. The income derived by such agencies from such projects shall be exempt from all taxation now or hereafter imposed by the United States.