Treasury has really been giving noogies to banks and brokerage firms about compliance with Know Your Customer paperwork like this form. The fines for non-compliance are preposterous, like $10,000 per customer account. It's not only domestic US banks, either; under the FATCA program asserting worldwide imperial jurisdiction, every institution that wants to do any business in or with the US has to provide these forms for every known or suspected US person on their customer list, along with reporting of assets and income. My broker in Hong Kong emailed me all in a swivet last March, demanding a scanned W-9 right away. They knew I was a US person, but they felt they needed the right form!