Every registered taxable person - who crosses the threshold limit for payment of taxes. A supplier needs to be registered when the aggregate turnover crosses Rs. nine lacs but he become taxable person ONLY when he crosses Rs. ten lacs. So he will be required to file returns when he crosses the threshold limit of Rs. ten lacs. There are some other class of persons who need to be registered and therefore will have to file returns like interstate suppliers, TDS deductors, e-commerce operators, suppliers supplying goods through e-commerce operators etc (reference Schedule-III and Question 6 of the Registration Chapter).