Overdraft Protection Options-Increasing Fee

We currently offer two overdraft protection options - one is a transfer from a line of credit and the other is an auto transfer from a deposit account. In either case, we have a disclosed transfer fee of $5.00 per transfer which is charged to the checking account regardless of whether the funding account is the LOC or the deposit account. We would like to increase the fee on existing accounts. Because we charge the same fee (whether it is a LOC transfer or a deposit account transfer) to the checking account is it possible to increase the fee with a 30 day notice to customers like any other fee adjustment? We are also considering an annual fee for this service for both new and existing customers. The annual fee would be charged to the checking account and not to the LOC/funding account.