Passengers check in at a counter of Delta Air Lines in Mexico City, Mexico, August 8, 2016. REUTERS/Ginnette Riquelme/File PhotoWASHINGTON (Reuters) – U.S. imposition of tariffs against the European Union over aircraft subsidies would cause “serious harm” to Delta Air Lines since the U.S. carrier is already under contract to buy several billion dollars worth of Airbus aircraft, a senior airline official said on Wednesday. Delta Associate General Counsel Scott McClain told a hearing that the airline was contractually obligated to pay for any tariffs imposed. He said the U.S. tariffs “will not punish the foreign producer because we can’t avoid those orders now.” Instead, it would force Delta to pay what he called an “unexpected tax” that would harm the airline, its employees and its customers. Reporting by Andrea Shalal; editing by Jonathan OatisOur Standards:The Thomson Reuters Trust Principles.