Shadow treasurer Tim Wilson is planning a half-trillion-dollar hit to the budget bottom line, Jim Chalmers said, as the government faces backlash over winding back tax concessions for investments in property, shares and trusts.
Costings released by the treasurer show repealing the changes - as the coalition has promised - would cost the federal budget $544.4 billion over the next nine years.
That includes $212 billion in lost revenue from indexing income taxes, $43.1 billion from repealing the capital gains tax and negative gearing reforms, and $44.2 billion from scrapping the new tax on trusts.
Other hits include $93.5 billion on increased defence spending and $50 billion slashing Australia's migrant intake.
But the benefits young people will get from Labor's tax policies relied on an accurate understanding of where Australians kept their money, Mr Wilson said.
And he said the government has got it all wrong.
More than 85 per cent of Australians under 35 had money invested in shares, the shadow treasurer said.
The government claims the figure is closer to 10 per cent.
"He either doesn't know the real figure, or more likely he's lying about that as part of this desperate scare campaign against these sensible changes and sensible reforms in the budget," Dr Chalmers said.
While the coalition would make savings from scrapping various measures, including a tax discount on electric vehicles and a key housing fund, the government's figures suggest it would not come close to offsetting the extra spending.
"This is a multibillion-dollar debt bomb that the coalition would drop on future generations of Australians," Dr Chalmers said.
"Their uncosted policies would deliver much bigger deficits, higher debt and higher inflation."
Some of the figures Labor has relied on for its costings date back to commitments made in 2022.
The government says this makes its estimates conservative.
The treasurer told reporters on Monday the coalition was likely to vote against the measures, suggesting it had not learnt since voting against tax cuts in the previous term of parliament.
"In the first term, they voted against housing, they voted against tax cuts,'' he said.
"They're showing every sign of having not learned a thing or changed a bit since the first term, when they made those mistakes, saying that they will vote against housing and vote against tax cuts."
Mr Wilson rejected the government's claims, accusing Labor of planning to slug Australians with billions of dollars in higher taxes.
"Jim Chalmers and Anthony Albanese have admitted they're hitting us with $273 billion in taxes Australians didn't vote for," he said.
Mr Wilson's figure is based on Labor refusing to back the coalition's plan to index income tax brackets in line with inflation, as well as the government's planned changes to negative gearing and the capital gains tax.
Parliament resumes on Tuesday for three sitting days, with debate over the tax reforms likely to take centre stage as the government seeks to have the legislation passed before the lengthy winter break.
The coalition is threatening to withhold support for separate legislation tightening eligibility for the National Disability Insurance Scheme if Labor tries to pass its tax changes with the support of the Greens, paving the way for messy negotiations in the coming days.