PAN furnishing requirement triggers higher tax withholding when PAN is not provided, with limited statutory exceptions. Requirement to furnish a Permanent Account Number (PAN) obliges deductees to provide PAN to deductors; absence or invalidity of PAN mandates tax deduction at the higher of the statutory rate, the rate in force, or a specified higher rate. Declarations and certificate applications are invalid without PAN; an invalid PAN is treated as non-furnishing. PAN must be quoted in all correspondence and documents. The section exempts certain payments to non-residents and foreign companies subject to prescribed conditions.