Treasurer says super caps a 'tweak', not major reform

The treasurer has defended possible changes to tax breaks on multimillion-dollar superannuation balances as reasonable measures that won't alter the fundamentals of Australia's retirement savings system.

Jim Chalmers said the changes under consideration, which could include a cap on large super balances attracting concessional tax treatments, were not "especially controversial".

He said they were similar in scope to "tweaks" made by the former coalition government while in office, including changes to superannuation taxes in 2016 that raised $5 billion.

"So the fundamentals won't change - the tax concessionality will still be there, but we do need to consider whether we can afford the degree of tax concessionality for people who've got very big balances," he said.

Dr Chalmers said he hadn't been considered or working on changes to superannuation taxes for long, but they had consistently been recognised as a pressure on the budget.

He also denied the possible changes to top-end concessional treatment would be the first of many changes to the super system under Labor, as suggested by former Liberal prime minister John Howard.

"I'm not interested in a war of words with John Howard - John Howard is someone who I respect and he deserves better than to be wheeled out to prop up (shadow treasurer) Angus Taylor's dodgy arguments or to shore up (Opposition Leader) Peter Dutton's failing leadership," he said.

But Mr Taylor said Mr Howard had spoken of his own volition and had identified a genuine breach of trust from the government.

"The point he made is this will just be the beginning for Labor," he said.

Mr Taylor added Dr Chalmers was failing to exhibit "sustainable" spending patterns by pushing $45 billion in off-budget spending through parliament.

"This is just not the right time - we've got inflationary pressures, and interest rate pressures, and that's something that he doesn't seem to want to talk about if he can avoid it."

The Greens and key independents, who are needed to pass legislation through the Senate, have said they are open to limiting tax concessions for people with large super balances.

Greens leader Adam Bandt said the party would look at any proposal the government landed on and consider it in good faith.

But he is worried the money saved from winding back tax concessions will be used to fund stage-three tax cuts, which will effectively flatten the tax structure for people earning between $45,000 and $200,000.

"Our concern is that the government might be robbing Peter to pay Paul and winding back some concessions for high-income earners to fund $9000-a-year tax cuts for politicians and billionaires while everyday people get left behind," Mr Bandt said.

Federal ministers have been alluding to possible changes to super concessions for months, but the discussion ramped up last week with a proposal to enshrine an objective for superannuation into legislation.