We believe that a bank must obtain taxpayer identification numbers (TINs) when any customer opens an account, regardless of the customer’s status as to a joint account. Whether the bank needs to obtain a taxpayer identification number when an existing customer opens a new account is up to the bank.

When a customer opens a new account, the bank’s Customer Identification Program (CIP) must, at a minimum, require that the following information be obtained from the customer: (1) name, (2) date of birth (for individuals), (3) address, and (4) taxpayer identification number. 31 CFR 1020.220(a)(2)(i). The bank’s CIP may require customers to provide additional information. A “customer” includes any person opening a new account, but the term does not include “[a] person that has an existing account with the bank, provided that the bank has a reasonable belief that it knows the true identity of the person.” 31 CFR 1020.100(c)(1)(i). (The term “person” includes individuals and legal entities. 31 CFR 1010.100(mm).)

Further, you are required to put the taxpayer’s identification number on the IRS Form 1099-INT when reporting interest income. See this sample 1099-INT form.