Apparently Citibank asserts the "right" to keep customers from withdrawing their accounts without seven days notice.  Some Citibank account holders have received notices reminding them of an existing Citibank policy.  The policy as taken from their website reads:

"Withdrawal Notice
We reserve the right to require seven (7) days advance notice before permitting a withdrawal on all checking, savings and money market accounts.  We currently do not exercise this right and have not exercised it in the past."

Let me know if you know of any other financial institutions that have this policy.