Service tax exemption

One of My client being an Individual as Service Provider engaged in Taxable services "Erection,Commissioning & Installation".

At present he is Providing Services to Adani Power Ltd being a Co as Developer of SEZ units like Mundra Port SEZ LTD since April,2011 & Onwards.(i.e. whithin Premises of SEZ Area & exclusively for their Consumption.)

As per Service Receipent they are exempted from Service Tax as per Certificate issued by Development Commissioner under Ministry of Commerce & Industry.

Now query is whether My client ie Service Provider is exempted from Service tax under the Above Catogery & If Yes the Under What Notification of Service Tax Act/Rules.

Please reply at the earliest as the Ist Half yearly ST 3 Return for the Period ended on 30/09/2011 is going to be filed on or before 25/10/2011 online.