21. Levy and rate of tax on works contract
(1) The tax payable by a dealer, who is liable to pay tax under section 15, shall be levied at the rate of four per centum of that part of his contractual transfer price of goods during any period which remains after deducting therefrom his contractual transfer price during that period on-
(a) contractual transfer of goods referred to in section 14 of the Central Sales Tax Act, 1956, (74 of 1956) on a prior sale whereof in West Bengal due tax under this Act is shown to the satisfaction of the Commissioner to have been paid;
(b) contractual transfer of goods, sales of which are declared tax-free under section 24;
(c) such other contractual transfers as may be prescribed:
PROVIDED
(a) where a declaration referred to in the first proviso to sub-section (2) of section 17, or a declaration referred to in sub-section (1) of section 6A of the Central Sales Tax Act, 1956 (74 of 1956), or a declaration or certificate referred to in sub-section (4) of section 8 of that Act has been furnished, or to be furnished, by a registered dealer to a dealer from whom goods have been purchased, or procured otherwise than by way of purchase, by such registered dealer for use by him directly in execution of a works contract, or
(b) where goods have been procured by a registered dealer from his contractee otherwise than by way of purchase for use by him directly in execution of a works contract,
the tax payable by such registered dealer executing such contract shall be levied at the rate of -
(i) five per centum of the contractual transfer price, wholly or partly, or printing materials involved in execution of such contract,
(ii) eight per centum of contractual transfer price of goods, other than those referred to in sub-clause (i), involved in execution of such contract.
(2) Where a dealer enters into a contract with, and engages, another dealer for execution of a works contract, whether in part or in full, the contractual transfer price relating to the execution of such works contract executed by that other dealer shall, subject to the production of the proof of payment of tax by that other dealer, be deducted from the contractual transfer price of the dealer who engages the other dealer for execution of the works contract.