1) the labour welfare cess is being collected by govt for providing welfare to unskilled workers
2) it is supposed to be 1per cent of construction cost levied on the builder
3) it is liability of builder to pay this tax for welfare to his labourer
4) since you have agreed to pay the labour cess under the agreement builder is seeking to recover the amount of cess from you
5) pay the amount under protest take possession of flat then move consumer forum against builder and seek refund as it is liability on the builder