Federal Opposition finance spokesman Andrew Robb has come out in support of the big banks raising rates outside of the Reserve Bank's recommendations.

Late on Friday, ANZ Bank announced it would raise its interest rates this month, becoming the first of the big four banks to move after the RBA left the official cash rate steady.

Treasurer Wayne Swan has condemned the move, saying ANZ customers should be upset given the bank's massive profits.

But Mr Robb says the bank would not have raised rates if it were not suffering a problem with its margins, and he blames government debt for the decision.

"They are not stupid and I don't think they would willy-nilly put up their margin like this if they weren't suffering a problem with their margins," he told AM.

"They are responsible citizens, their books in the end will be on the table with their profit margins and all the rest.

"I mean, look at banks that are heavily part of superannuation funds - millions of Australians depend on the banks performing."

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From April 20, ANZ bank will increase its standard variable mortgage rate by 6 basis points to 7.42 per cent per annum.

The bank said it took the decision because its funding costs were rising due to increased competition for deposits.

Westpac's standard variable mortgage rate is 7.46 per cent, Commonwealth Bank's is 7.41 per cent and NAB's is 7.31 per cent.

But analysts are warning that the other big banks are reviewing their rates.

It is the second time this year that ANZ has hiked its rates despite the central bank leaving the cash rate unchanged since December last year.