Dankse Bank, which is shutting its personal banking this year, has told customers it will only provide one statement a year to mortgage customers.
Previously customers were able to continuously monitor how much they owed.
The bank currently provides electronic banking which allows customers see the full extent of their borrowings. But this service will be switched off under its current plans.
One customer who queried how frequently they would be able to find how much they owe was told: "There is currently no change to the frequency of your mortgage statements. At present, you will receive one statement annually."
However, a spokesman for Danske Bank said the lender has made "no decision in relation to what arrangements will be put in place for mortgage customers seeking information on balances."
He added the bank expects to formally write to all mortgage customers by the end of January.
He said this would include details on how customers will access balance information in future.
He said any arrangements put in place will be done so in line with relevant regulatory requirements.
It is understood banks are required to provide annual statements.