Reimbursements to any worker, including firefighters, made under an accountable plan are not subject to tax and withholding. An accountable plan must require workers to substantiate business expenses, allow no reimbursement for unsubstantiated expenses, and require the employee to return any amounts reimbursed over documented expenses to the employer within a reasonable period. Any amounts reimbursed to employees that do not meet these conditions are considered wages subject to all the taxes discussed above. It does not matter whether the amount is labeled per call, per diem, or any other description: it is still taxable.