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.