Is subcontractor doing services to government liable

HAI SIR,

MY CLIENT DOING SUB-CONTRACTS TO A MAIN COMPANY WHICH GOT CONTRACT FROM GOVERNMENT RELATING TO DAM AND CANAL WORKS.  WHETHER MY CLIENT BEING A SUB CONTRACTOR LIABLE TO PAY SERVICE TAX OR HE CAN ALSO BE COVERED UNDER NEGATIVE LIST OF SERVICES(12(d)), BEING ULTIMATE SERVICE TO GOVERNMENT?

SAME CLIENT IS ALSO DOING SERVICE AS A SUB-CONTRACTOR TO A COMPANY,WHICH GOT THE WORK FROM RAILWAYS. IN THIS SITUATION ALSO, CAN MY CLIENT CLAIM THE SERVICES EXEMPT(14(a)) BEING LISTED IN NEGATIVE LIST OF SERVICES?

PLS ADVISE?