Shadow treasurer Chris Bowen has pledged Labor will scale back the overly-generous tax concessions of the Howard government era.
Labor has already put forward numerous proposals, including restricting negative gearing and halving the capital gains tax discount, while opposing the Turnbull government's $65 billion business tax cuts.
But Mr Bowen told a conference in Melbourne on Monday the tax base remains full of holes and tax concessions and other loopholes go unreformed.
"The Howard-Costello government locked in unsustainable spending and tax concessions when the budget was being hit with gold bars during the mining boom," Mr Bowen told the Per Capita conference.
He says the coalition has barely taken a scalpel to the Howard government tax concessions that mostly benefited wealthier Australians.
"We recognise that dealing with these structural problems in the budget opens us to the usual scare and misinformation campaigns from the government," Mr Bowen says.
"But good policy will win out."
Mr Bowen would not be drawn on specific tax concessions when quizzed by reporters after his speech.
"If there's things in the budget which benefit high-income earners in particular then they need to be considered," he said.
"That's the approach we've taken with family trusts, with negative gearing, with capital gains tax, and we will continue to do that and we have more to say in terms of detailed policy announcements."
Treasurer Scott Morrison said Labor is asking for a "blank cheque" to drive up taxes.
"They will use any excuse to raise taxes," Mr Morrison told AAP.
"Having lectured the government on the need to keep taxes as a share of GDP down, they have abolished their own commitment to the very same standard."
Treasury boss John Fraser and the Parliamentary Budget Office told Senate hearings last week the government's business tax cuts are fully factored into the budget.
But Mr Bowen argues just putting something in the budget does not mean it is funded.
He said on that logic, the government's argument that Labor's Gonski school funding reforms and the national disability insurance scheme wasn't fully funded falls apart.
"Labor did make cuts to fund things," he earlier told ABC radio.
He said the budget would be $65 billion better off over the decade if the corporate tax cuts did not proceed.
Nor is he is yet satisfied the return to surplus is locked in as it should be with the government's prediction of wage growth bouncing back an "optimistic assumption".
"The government that once warned us about a budget emergency and a debt and deficit disaster is engaging in a fiscal ram-raid, hitting the budget with $65 billion in a way which in our view is unsustainable and there are better priorities," he said.
