Generally, individuals evacuated on a U.S. government-coordinated transport, including charter and military flights or ships, even if those transports are provided by another country’s government, must sign an Evacuee Manifest and Promissory Note (Form DS-5528) note prior to departure. The Department of State uses the Form DS-5528 to document who got on which transport, and it lets us know how to contact evacuees for billing purposes.

U.S. law requires that departure assistance to private U.S. citizens or third country nationals be provided “on a reimbursable basis to the maximum extent practicable.” By taking a U.S. government coordinated transport, evacuees are obligated to repay the cost of their transportation. The amount billed to evacuees is based on the cost of a full fare economy flight, or comparable alternate transportation, to the designated destination(s) that would have been charged immediately prior to the events giving rise to the evacuation.

https://www.govinfo.gov/app/details/USCODE-2017-title22/USCODE-2017-title22-chap38-sec2671