A FATCA letter typically comes from a Foreign Financial Institution (FFI). The letter will contain a request for information about your tax filing status within the United States. Along with the letter, you may also receive certain forms that your FFI requests be returned, including a W-8 or W-9 form. The purpose of these forms is to confirm your status as a United States taxpayer so the FFI can make a determination regarding whether the bank must provide information about your accounts to the United States taxing authorities.