If your business does *NOT* have an accountable plan, then what you reimburse the employee gets included in box 1 of their W-2 as wages paid.
If your business does have an accountable plan, then the employee is required to submit receipts for reimbursement. The amount reimbursed is "NOT" reported to the employee on their W-2 or any other type of tax reporting document. But for the business it is a valid and deductible business expense. (Transportation expense I"m guessing?)
