The major banks and credit unions have increased credit card interest rates by up to four times the Reserve Bank's official rate rise, according to source research firm Cannex.
National Australia Bank passed on larger than official rate increases to its customers since the official rate rise.
On May 15, it raised its rates on gold rewards cards by 0.85 percentage points - more than three times the 0.25 percentage point rate rise on May 3.
Rates on other NAB cards, including standard Visa and Mastercards, were increased by 0.34 percentage points.
The country's big credit unions managed to get their rate rises in place in April before the RBA move, raising the rate on the national MyCard Mastercard by 1 percentage point.
St George, Westpac, ANZ and Commonwealth Bank have only introduced rate increases of 25 basis points in line with the official rate rise.
The news is better for Queensland consumers after Suncorp slashed 1.95 percentage points from the rate of its Suncorp Clear Options Standard Visa card on May 15. Bank of Queensland was in line with the RBA rise, but raised two of its products by only 20 basis points.
Australian Consumers' Association senior policy officer Nick Coates says those institutions raising rates above the official ones are "price gouging".
"We believe that when there is an official increase of one quarter per cent the banks and other card issuers should not be allowed to make higher increases," he says.
"This behaviour suggests that some banks are using credit card customers to claw back revenue they lost as a result of the RBA's recent clampdown on bank interchange fees."
NAB head of cards Andrew Maitland defended the rate rises on gold cardholders, asserting in a statement emailed to The Courier-Mail that rival products marketed by ANZ and Commonwealth Bank carried higher rates.
NAB spokeswoman Kerrina Lawrence says different percentage increases were passed on to cardholders depending on the competitive position of each product in the market.
"It takes into account the RBA's rate rise and NAB's competitive position," she says.
CUSCAL, which represents 85 per cent of Australian credit unions, yesterday distanced itself from the decision to raise rates on credit cards marketed by its members.
The head of public affairs at CUSCAL, Julie Sheather, says the move to increase rates was made by Citibank which is the official issuer of the MyCard product marketed by credit unions.
Since acquiring the CUSCAL credit card business in May 2004, Citibank has assumed control over interest rate decisions.
The ACA's Mr Coates queries the size of the rate hikes on credit union Mastercards.
"We would like to think that alternative financial institutions bring greater competition to the marketplace because they need to be able to break down some of the pricing structures existing between the banks."
The higher-than-expected rate increases come as banks' reputations are again under pressure.
Nielsen Media researches rolling survey says the average satisfaction reading for the four major banks slumped by 3 percentage points in the March quarter alone -- and higher fees and charges were to blame.
The average satisfaction reading for the four major banks has now fallen to its lowest in three years.
According to the Neilsen reputation survey, ANZ was the worst performer in the March quarter, falling 5.1 percentage points to a reading of 82.3 per cent.
In terms of poor performance for the quarter, it was followed by Westpac (which fell 3 percentage points to 77.8 per cent), Commonwealth Bank (down 2.8 percentage points to 72 per cent) and National Australia Bank (down 1.3 percentage points to 77.8 per cent).
