Answer:
One of the "Best Practices" listed in the Joint Guidance on Overdraft Protection Programs, published on February 24, 2005, is "Alert consumers before a transaction triggers any fees." While the regulators' preference stated in the Guidance is that specific notices be given if possible, a general statement could be used (for example, at ATMs) explaining that transactions may be approved that overdraw the account and fees may be incurred. This Guidance is still in effect.
As you mentioned, there may be more specific state requirements.