Service tax Applicability of RCM on Work contract services to Govt - Goods and Services Tax - GST

Dear Experts, One of our client is under appeal in service tax matter and they are liable to discharge tax on certain taxable works contract services which was not done by them. However, IO has computed 100% tax liability liability in hands of contractor under forward charge but as per ST Notification no. 30/2012 , there was 50% reverse charge on work contract services. The recipient in our case is government and therefore my question is whether there was any exemption under service tax as per which Govt was not liable to pay RCM on works contract and 100% was payable under forward charge by contractor?