Labor Law Question: XX

"A", a driver for a bus company, sued his employer for nonpayment of commutable service incentive leave credits upon his resignation after five years of employment. The bus company argued that A was not entitled to service incentive leave since he was considered a field personnel and was paid on commission basis and that, in any event, his claim had prescribed. If you were the Labor Arbiter, how would you rule? Explain. (6%)