Charges for unpaid and part paid mail

§ 4110. Charges for unpaid and part paid mail The Postmaster General shall prescribe from time to time the charges to be collected for matter mailed without prepayment of required postage. The charges— (1) shall be in addition to the payment of lawfully required postage, (2) may not be adjusted more frequently than once every two years, and (3) when adjusted, shall equal, as nearly as practicable, the approximate cost incurred by the Department with respect to the delivery of such matter and the collection of postage and other charges thereon. The Postmaster General may waive the collection of any charges when he deems a waiver to be in the interest of the Government.