Consumer journalist and The Home Show host Sinead Ryan says variable rate mortgage customers with KBC Bank could be in for a shock.
KBC announced it was to leave the Irish market earlier this year.
The Belgian bank is moving its performing loan assets and liabilities to Bank of Ireland, after the two banks entered into a memorandum of understanding (MoU).
But Sinead told Lunchtime Live that KBC mortgage customers should keep an eye on what's happening.
"KBC customers are in the somewhat enviable position in that they have been sold lock, stock and barrel - if you like - to Bank of Ireland.
"So Bank of Ireland are taking over current accounts, deposit accounts and mortgages.
"So a lot of KBC Bank customers will feel possibly 'That's great, that means I don't have to do anything'.
"And for a lot of them that will be the case.
"However, for about 40,000 homeowners, their move to Bank of Ireland they just might have to think twice about what's happening.
"If you're on a fixed rate with KBC currently, and you move to Bank of Ireland - irrespective of anything - they must maintain that contract for you until it's up.
"For variable rate customers, they're going to move off KBC's nice low variable rates - which start at about 3.05% - and they're going to move on to Bank of Ireland's not-so-nice variable rates.
"And they might be in for a bit of a shock then: Bank of Ireland can - they haven't said that they will - but they can change variable rates anytime they like, and that'll affect all customers.
"And for any of those KBCs coming off contract... they're going to be pushed back into the variable rate market as well.
"I'm not saying 'panic' or rush to do anything, but just be conscious and aware that your mortgage will change."
But she says people should consider changing banks regularly.
"It's a ripe opportunity for anybody, of any bank, who is a customer to look at switching.
"In fact I would recommend people look at switching every few years - regardless of who they're with and what contract they're on.
"The good news is the banks are all vying with each other, it's a very vibrant market - despite KBC leaving and Ulster Bank leaving".