PAN requirement: taxpayers who have linked Aadhaar may furnish Aadhaar instead of PAN where PAN is mandatory for transactions. Quoting PAN is mandatory on the return of income and on tax payment challans and correspondence; where a person has been allotted PAN and has linked Aadhaar to that PAN, the taxpayer may furnish the Aadhaar number in lieu of PAN for transactions where PAN is mandatory.