Zero rated sale

hi

we are supplying fabrics to export oriented companies in india from last 30 years. we did not take any tin number as we fall under zero rated sale and hence don't need to pay any VAT. but now the local tax authorities are pressurising for taking tin number without showing any circular or notice. Is it now mandatory to get a tin number even for zero rated sale ? my business is located in chennai. please clarify. thank you.