Sec. 40(a)(ia) applies not only to assessees following mercantile system but also to assessees follo

IT : Requirement to deduct tax at source under section 194C is mandatory and, in case of assessee's failure to do so in respect of contractual payments, disallowance has to be made under section 40(a)(ia) irrespective of fact as to whether assessee is following cash or mercantile system of accounting