Some accounts are designed to be non-transaction 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.  When you have reached your transfer limit you will receive a message informing you that no more transfers are allowed.

You can make up to six withdrawals a month from your savings account, 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 or by mail.

This is a Federal Regulation which the Credit Union must abide by.  If you have alternate savings accounts established within the same membership account, you are allowed to make six withdrawals as explained in the above paragraph per each alternate savings account.