Some accounts are designed to be non-transacation accounts and others are designed to be transaction accounts. A checking account is a transaction account, a savings account is a non-transaction account.  Regulation D prohibits excessive withdrawals/transfers from non-transaction accounts like savings accounts.

You can make up to six withdrawals a month from these accounts, including transfers to another account, pre-authorized transfers, overdraft protection transfers, automatic transfers, recurring payments, telephone transfers/withdrawals, and Internet transfers/withdrawals. This limit does not include withdrawals made at an ATM, in person, by mail or by telephone if a check is mailed to your home.

An Overdraft Protection Transfer Fee anytime an Overdraft Protection Deposit is posted to your Checking account to cover an overdrawn balance, as already indicated on your Schedule of Fees and Charges under Forms & Disclosures. To avoid this fee, you can transfer the necessary funds yourself using anytimeBanking or TouchTeller prior to the posting of the transaction.