Bank customers in Northern Ireland appear to be paying higher charges than those in Britain, a report has said.
NI's four main banks have been criticised for overcharging customers
The Competition Commission said it may be due to a lack of proper competition between the big four NI banks.
A so-called super-complaint over the charges was lodged with the Office of Fair Trading and the commission has been investigating bank services.
It said customers may be paying higher charges and getting lower rates of interest than they should.
The level of charges imposed by the big four Northern Ireland banks - Bank of Ireland, Ulster Bank, First Trust and Northern Bank - on current accounts sparked complaints by consumer groups.
A super-complaint was lodged by the Consumer Council and Which? magazine about 17 months ago.
In an interim report, the Competition Commission said despite change by some but not all of the Northern Ireland banks, competition between them may not be fully effective
It also noted a low level of switching of accounts and that if one bank increased its charges the others tended to follow and prices converged to similar levels.
In a statement, Steve Costello of the Consumer Council said the report was an "indictment of the anti-competitive behaviour of the big four banks".
"It is powerful evidence that people here pay more and get less on their personal current accounts," he said.
"Consumers deserve fair, competitive banking that works for them, not against them.
"The banks must change this shameful treatment of customers now before they are forced to change."
The commission says it will be taking further evidence before it publishes its final report.
In a statement, Ulster Bank said it "strongly believes that the personal current account market in Northern Ireland has never been more competitive".
The bank said it had "radically overhauled" its personal current account charges last year, insisting that it listened and responded to "customer need".