Originally Posted by
stifle
IATA rules are all well and good but are an agreement between carriers. The agreement between the carrier and the passenger is the carrier's conditions of carriage. And the conditions of carriage allow the carrier to sue the passenger for the excess fare in this instance.
The airline has an obligation to remove the pax from the country they cannot enter, as directed by that country's authorities. The airline must do this, regardless of whether anyone can pay them. The delivering carrier erred by permitting an inadmissible pax to board.
IATA has an agreement to split the cost of doing this among the delivering carrier(s) should it happen.
The operating carrier can, under its contract of carriage, pursue damages from the passenger for the costs it incurs. In practice, this last step almost never happens because (a) in the case of a round-trip ticket, the return coupon is normally used, and (b) I would imagine in most other cases, the pax can obviously not afford the additional cost, so it's not worth pursuing.