You get a letter in the mail from your bank telling you that they are closing your checking account, your savings account and canceling your credit card, without explanation.
Or worse, you are in the grocery store buying food for your family and your card is inexplicably denied.
The bank won't provide any information, and you are left without a checking account, and no credit card.
What happened? Well, the bank thinks you are doing something suspicious. In my practice I occasionally see this when a client is involved in an SEC investigation. Presumably the bank gets a subpoena from the SEC, and gets concerned about its own involvement in the account. Since they don't need a reason to close an account, they close it. Without explanation.
The New York Times has an excellent article on the issue, and is looking for input from those who have been in this situation.
