Applicability of service tax on labour contarct bill

I am working with cable manufacturing unit and out source labour from outside contractor for operation of machines, loading, unloading, and packing of cables. contractor supllied us manpower on daily basis, and raised their bill for same at the end of maonth without charging the service tax, our products are covered under  central excise act 1944

if I asked to our contractor for issue of their bill with service tax, same will be allowed for cenvat credit to us

please guide us