Where the Canteen Stores Department of the Government of India makes sales of any taxable goods purchased by it in West Bengal, to a Regimental or Unit-run Canteen attached to the military units in West Bengal, such Canteen Stores Department may, for the purpose of determination of its turnover of sales on which tax is payable, deduct under clause (c) of sub-section (1) of section 16, from its turnover of sales that part of such turnover of sales which represents sales made to such Regimental or Unit-run Canteen, and it shall, on demand by the appropriate authority under the Act, furnish the relevant tax invoice, invoice, cash memo or bill, as the case may be:

Provided that no such deduction shall be allowed unless the dealer selling such goods, on demand by the appropriate authority under the Act, furnishes the relevant tax invoice or invoice or cash memo or bill.