Service tax on flat

Hello Sir,

I booked the 2BHK flat in Pune in June 2010 @ Rs.1800000/-. I'll get the possession of the flat in next 8-10 days. Now builder is asking me to pay Service Tax of Rs.40000 on the amount I already paid to him till date and on the amount I suppose to pay him at the time of possession.

Kindly advice me in case I liable to pay service tax to the builder EVEN IF I have not yet get the flat possession.

Thanks in advance