41 C.F.R. § 301-51.1

Employees are required to use the Government contractor-issued travel charge card for all official travel expenses unless:

(a) Payment through the card is impractical (e.g., a vendor does not accept the travel charge card) or imposes unreasonable burdens or costs; or

(b) The Administrator of General Services or the agency head or their designee has granted an exemption under § 301-51.2.