(B) Failing to provide return transportation or pay for the cost of return transportation upon the end of employment, for an employee who is not a United States national and who was brought into the United States for the purpose of working on a U.S. Government contract or subcontract, if the payment of such costs is required under existing temporary worker programs or pursuant to a written agreement with the employee for portions of contracts and subcontracts performed inside the United States; except that—