American Express Global Business Travel in an August letter indicated customers would pay a $10 surcharge on transactions booked with airlines deemed "high cost."

"This additional $10 fee applies to any transaction booked with a supplier that is booked outside a GDS; does not settle its accounts through industry-standard methods; has limited or no participation in industry-standard fare filing processes; or is designated as basic booking, low cost, specific or other similar designation," according to an Aug. 8 letter addressed to clients and obtained by The Company Dime.

Included among these suppliers are Aeromar, Dragonair, Frontier . . .

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