Labor is hoping to neutralise the government's tax cuts and cash splashes while promising Australians it will spend more on the services that matter to them.
But it has seized on the government's Wednesday morning change to extend power bill relief payments to those on Newstart - less than 12 hours after the budget papers excluded them.
Shadow treasurer Chris Bowen moved to suspend standing orders as soon as parliament kicked off on Wednesday, accusing the government of changing its budget at a cost of $80 million.
"The government's budget is unravelling less than 24 hours after it was delivered," he told the chamber.
"I've seen some budgets unravel in my time ... but never before have I seen a budget unravel quite as spectacularly or quickly as this."
Last year's $530 tax offset for low- and middle-income earners was doubled in Tuesday night's budget to $1080 for more than 10 million taxpayers earning up to $126,000 a year.
Opposition Leader Bill Shorten says the government has just matched what Labor promised a year ago.
"On the first of July, all Australians can know that whoever wins the election that they're going to get those tax cuts," he told reporters in Canberra on Wednesday.
Mr Shorten also pointed out the government's entire tax plan was two elections away.
"Who really believes this government will be around in two terms time to honour tax cuts which are in the middle of the 2020s?" he asked.
Even though the tax cuts for low- and middle-income earners could pass parliament this week with Labor's support, the coalition isn't willing to put them to a vote before the election.
The budget papers predict surpluses from next financial year, starting with $7.1 billion in 2019/20.
But the government faced criticism that the surplus was built on a $1.6 billion underspend on the National Disability Insurance Scheme.
Mr Shorten said that was one of the budget's more shameful features.
"I know people with disability and I know their families. I know there's many families crying out for support to which they're entitled and not getting," he told Sky News.
"I don't think they'll be very happy that the government's trying to write a political dividend from them."
Prime Minister Scott Morrison said it was a terrible lie to say there was an underspend.
"We overestimated the demand in the NDIS - that money actually shows up in extra expenditure on hospitals where a lot of those services are being provided by the states," he told ABC radio.
"So it's just swings and roundabouts."
