Filing obligation expanded: persons whose income exceeds the non-taxable limit must file returns by the due date. Section 139 is amended to treat companies and firms alike in specified clauses and provisos, to revise the first proviso's electricity expenditure wording and omit a clause, and to add a proviso requiring individuals, HUFs, AOPs, BOIs and artificial juridical persons whose total income, without applying sections 10A/10B/10BA or Chapter VI-A, exceeds the maximum non-taxable amount, to furnish a return in the prescribed form and manner on or before the due date; a date in sub-section (9)'s Explanation is advanced to 1 April 2006.