The proposed acquisition by AIB of a portfolio of performing Ulster Bank mortgages has been notified to the Competition and Consumer Protection Commission.
The portfolio of performing residential loans are mainly tracker mortgages.
In April, AIB had said it has started exclusive discussions with NatWest for the acquisition of about €6 billion of Ulster Bank's performing tracker mortgages.
The bank said that any potential transaction remains subject to negotiations and agreement.
It is believed that up to 40,000 tracker mortgages could be included in the sale.
The Competition and Consumer Protection Commission in April granted clearance for AIB's proposed purchase of Ulster Bank's €4.2 billion performing commercial loan book.
This comes as Ulster Bank continues its phased withdrawal from the Irish market.