The Abbott government's commission of audit says it could still recommend changes to the goods and services tax, even though the coalition remains adamant it will not alter it.
Chairman Tony Shepherd says "everything is on the table" as his commission looks at all areas of government before making recommendations on how to deliver a sustainable budget surplus of one per cent of GDP by 2023/24.
Mr Shepherd told a Senate inquiry into the audit on Wednesday the commission has a broad remit.
Asked by Labor senator Sam Dastyari whether he stood by his previous public comments, as Business Council president, that the GST rate should be raised and its base broadened, Mr Shepherd said he had an open mind.
Since the election the government has been firm the 10 per cent consumption tax would not be changed in any way.
But when quizzed on whether changing the GST could be recommended by the commission, Mr Shepherd said: "I'm not ruling anything in or out. Everything is on the table.
"The government is well aware of the revenue side of the situation and it's up to them to make the decisions as to what part of any solution that revenue would be," he said.
A spokeswoman for Treasurer Joe Hockey said the GST would not change under the coalition, "full stop, end of story".
"It's reckless to speculate over the findings from an inquiry that hasn't even finished yet," the spokeswoman told AAP.
Mr Shepherd said there were no "no-go areas" for the commission, and also refused to rule out recommending the sale of public assets or welfare changes.
Past privatisations have been overwhelmingly successful, he said, and any future asset sales should be based on facts.
While he did not believe the final audit report should be made public, the decision was up to the government.
Earlier Mr Hockey described the inquiry as a "stunt" by the opposition.
"Let them (the commissioners) get on with doing the job," Mr Hockey said.
Opposition Leader Bill Shorten said Australians had a right to know what would be cut as a result of the audit.
The inquiry was told a budget surplus of one per cent of GDP within a decade was an "achievable and fair target" for Australia.
Australia faced the challenges of an ageing population, poor productivity, a persistently high Australian dollar, high energy costs, heavy reliance on the resources sector and a volatile global political and economic outlook, Mr Shepherd said.
"The magic pudding is a fable and unless we fix this problem now we will consign to our children and their children the legacy of unsustainable largesse," he said.
The commission's initial report, on the financial position of the commonwealth and the budget's sustainability, will be provided to the government at the end of this month.
A second report, on infrastructure, public sector performance and accountability, is due by the end of March.
The findings of the report will be incorporated in the May budget.
The commission has received more than 300 submissions and Mr Shepherd has met with several premiers and department secretaries, as well as bodies such as SBS and Australia Post.