Treasurer Josh Frydenberg has asked the competition watchdog to investigate the banking sector over its refusal to pass on interest rate cuts to customers in full.
Since January, the Reserve Bank has reduced the official rate three times to a new record low of 0.75 per cent.
Mr Frydenberg said that the big four banks failed to pass them on in full.
The big four banks have passed on the equivalent of three quarters of the RBA cuts.
"It's costing someone with a $400,000 mortgage around $500 in higher interest payments than they otherwise should have to pay if these last three rate cuts were passed on in full," Mr Frydenberg told Channel 9.
"But it's not just these last three rate cuts where the banks have failed to pass them on, it's actually what's happened previously under the Labor government, there were 14 different rate cuts and only five of them were passed on in full.
