39 U.S.C. § 3683 — Uniform rates for books; films; other materials

(a) despite any other provision of this title, the rates of postage established for mail matter enumerated in former section 4554 of this title must be uniform for the mail of the same weight, and must not vary with the distance transported. (b) The rates of postage under former section 4554(b)(1) of this title must not be effective except about mailings which— (1) constitute materials specified in former section 4554(b)(2) of this title ; and (2) are sent between— (A) an institution, organization, or association listed in subparagraph (A) or (B) of the former section 4554(b)(1) and any other the institution, organization, or association; (B) an institution, organization, or association referred to in subparagraph (A) and any individual (other than an individual having a financial interest in the sale, promotion, or distribution of the materials involved); (C) an institution, organization, or association referred to in subparagraph (A) and a qualified nonprofit organization (as defined in former section 4452(d) of this title ) that is not the an institution, organization, or association; or (D) an institution, organization, or association referred to in subparagraph (A) and a publisher, if the institution, organization, or association has placed an order to purchase the materials for delivery to the institution, organization, or association.