Anon - it sounds like you hit the 6-transaction limit on a "non-transaction" account (something other than a checking account). Regulation D limits non-personal transactions on these types of accounts to 6 per month (3 per month for certain types).
"Non-personal" transactions include transfers to pay check overdrafts, internet banking transfers, telephone transfers, automatic debits to the power company and other vendors, and just about anything you request when you're not physically present at the bank or an ATM.
Check your account agreement, it will probably have more information about what kinds of transactions you can do on each type of account, and the monthly limits for each.
The purpose of the transaction limit required by the Regulation is to drive "transactions" through actual "transaction" accounts (i.e.: checking accounts).
All banks are required by the Regulation to hold reserves on all funds in transaction-class accounts to kind of "make up for" the way we give immediate credit on checks you deposit, but for which we haven't yet received the funds from the drawer's bank. It's a bit of a safety net in case something happens to the checks in transit from one to the other (on a large scale).
But what it comes down to is the Fed doesn't want savings accounts (not reserved) used as checking accounts (with reserves). And they make us monitor your account to make sure everyone's within limits.
Contact your branch manager to see what techniques you can use so you don't hit that 6-transaction mark. They may have options you are unaware of.
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Just a lowly 1st Year Law Student ("1L"), so don't take anything I say seriously!