Tax deduction at source on payments to non-residents requires withholding unless AO certifies exempt receipt. Payers to non-residents or foreign companies must deduct tax at source on interest or other sums chargeable under the Act at credit or payment; credit in books amounts to chargeable credit. A payer may apply to the Assessing Officer to determine the chargeable proportion so tax is deducted only on that proportion. A payee may obtain an Assessing Officer certificate permitting receipt without deduction while the certificate remains in force. The Board may prescribe rules, require information furnishing, and notify classes of cases requiring AO determination.