41 C.F.R. § 301-72.300

Agencies must establish administrative procedures providing-

(a) Written instructions explaining traveler liability for the value of tickets issued until used or properly accounted for on the travel voucher;

(b) Instructions for submitting payments received from carriers for failure to provide confirmed reserved space;

(c) The traveler with a “bill charges to” address, so that the traveler can provide this information to the carrier for returned or exchanged tickets; and

(d) Procedures for promptly identifying any unused tickets or other evidence of refund due the Government.