41 CFR 301-51.102: -51.102 Reimbursement for unauthorized cash purchases of common carrier transportation.

If an employee makes an unauthorized cash purchase of common carrier transportation, the agency may limit reimbursement to the cost of such transportation using the authorized method of payment.

(a) Limited reimbursement. For cash payments that an agency determines were made under non-emergency circumstances, reimbursement to the traveler is limited to the cost that would have been properly chargeable to the Government had the traveler used a government provided payment resource, such as an individual Government contractor-issued travel charge card, centrally billed account, or GTR.

(b) Full reimbursement. Agencies may choose to make full payment when circumstances justify it, such as for invitational travel, trips by infrequent travelers, and interviewee travel.