41 CFR § 301-72.204
What must we do to minimize the need for a traveler to use cash to procure common carrier transportation services?
June 9, 2020
You must establish procedures to encourage travelers to use the GSA individual Government contractor-issued travel charge card(s), or your agency's centrally billed or other established account, or a GTR (when no other option is available or feasible).
[FTR Amdt. 70, 63 FR 15976, Apr. 1, 1998; 63 FR 35538, June 30, 1998]