The Competition and Consumer Protection Commission says Ulster Bank and KBC customers need to switch before it's too late.
It's published a study today showing less than half of people, who need to switch, have done so.
That's despite both Ulster Bank and KBC preparing to exit the Irish market next year.
Grainne Griffin, from the CCPC, says one of the most awkward moves is switching all of your direct debits.
"They will understand why that's difficult.
"You only have so much money coming into your account, you might have a lot of different bills coming out.
"As you move from one bank to another, it's very important that everything moves over in the right order.
"Otherwise you risk not being able to make a payment on time such as a child maintenance payment or loan repayment."
