The Banking Ombudsman is investigating a wave of complaints regarding banks' mortgage break fees.
The office says it has received 100 complaints about the cost of repaying a fixed home loan early, covering a number of banks.
A break fee, or prepayment fee, is charged by a creditor to recover its loss when a customer repays their loan early.
Banking Ombudsman Liz Brown says her office is investigating the advice given by banks rather than the amount of the fee.
Ms Brown says there are cases where people feel they were misled about the likely cost or were poorly advised to enter into a fixed rate loan.
In other instances people were given an estimate of the break fee, but when they came to repay the loan, the fee was much larger than they had been told.
Liz Brown says her office received a similar raft of complaints in late 1990s, when interest rates dropped suddenly and unexpectedly .
The complaints are separate to a Commerce Commission investigation, which found the loan break fees charged by the country's four major Australian-owned banks were appropriate.