Consumer group Choice has lashed out at the major banks over their decision to slug customers with an extra charge when they use a rival bank's ATM.

From March 3 customers must be notified of charges before making a transaction at another bank's ATM, and then given the opportunity to pull out without being charged.

But National Australia Bank, Westpac, St George and ANZ have all announced extra fees which will not be shown on the ATM screen at the time of the transaction.

Commonwealth Bank says it is still considering its position.

The NAB will charge 50 cents per transaction, on top of the usual fee, while the others have not yet stated their price.

This means customers will be charged around $5 to check their account balance and make a withdrawal.

Choice spokesman Christopher Zinn says the new double fee lacks transparency, defeating the whole purpose of the laws in the first place.

"The point is that 50 cents isn't shown on screen, you only find out about it some weeks later if you peruse your statements," he said.

"It really is counter to the whole spirit, the whole idea of these reforms - that it will be transparent, to drive competition and to lower fees.

"This has the propensity to jack up ATM fees and that really clogs up the whole system."

He says if the big banks all decide to charge a 50-cent fee, it will add an extra $200 million to bank revenue each year.

"There are significant sums at stake. While the cost may be small to the individual, if you aggregate that up, how much you will pay over the year, that means that money is in the banks' pockets at the end of the year and not in consumers'," he said.

The new laws were brokered by the Reserve Bank of Australia to generate healthy competition between banks and keep consumer costs low, but Mr Zinn says that will never happen while the big banks maintain the lion's share of the market.

"The big four banks have far too much market power and concentration," he said.

"The banks always claim they have plenty of competition, we claim they move in lock step when it comes to many decisions.

"That's why we're so keen to make a real stand on this."

Mr Zinn says Choice is urging banks to stick with the spirit of the new laws and reverse their decision.

"It's quite simple, it's quite clear, it's what the RBA wanted, it's what everyone thought would happen," he said.

"When there's changes in fees being slugged here and there which are unnecessary, that just makes the hair on the back of our necks stand up, and it does so for consumers too."

He says people in remote areas, music festivals or nightclubs will be slugged the double fee because most of the time they have no choice but to use a rival or independent ATM.

"This is where people are going to need to be more alert. I've heard cases of people in small bowling clubs in the bush, the last place you'd expect to be gouged, charged $2.50 to find out their balance and another $2.50 to make a withdrawal," he said.

"That's the situation already, so people need to be aware of the cost that comes up on the screen."