Depending on who wins the July 2 election, high-income earners will either stop paying a temporary budget repair levy or face a permanent top tax rate of nearly 50 per cent.
But there's some confusion about the precise nature of the latter prospect with Opposition Leader Bill Shorten appearing to be at odds with his shadow treasurer.
Mr Shorten says the two per cent levy on incomes above $180,000 will remain in place for at least 10 years, possibly longer, while Chris Bowen says it will be made permanent taking the top tax rate to 49 per cent.
The coalition intends sticking by a legislated commitment to end the levy in mid-2017.
Mr Bowen told reporters in Sydney that tax relief across all income brackets would only be considered by a Labor government "when fiscal circumstances allow".
Mr Shorten said ending the levy was the wrong priority at a time of tough budgetary conditions.
The Labor leader also defended the decision to limit company tax rate cuts to small businesses with a turnover of $2 million, saying the budget can't afford Malcolm Turnbull's "cash splash".
The May 3 budget proposed a tax cut for small business from 28.5 per cent to 27.5 per cent from July 1, while expanding the definition of a small firm to $10 million from $2 million.
That definition increases incrementally each year, and by 2023/24 all businesses will pay 27.5 per cent instead of 30 per cent.
That rate will be reduced to 25 per cent in 2026/27.
"Mr Turnbull is making a promise which will permanently damage the underlying basis of our budget for the long term," Mr Shorten said.
He was asked how he could equate a local builder with an annual turnover of $4 million with a bank or a foreign shareholder, and whether there was room for a compromise to $5 million.
"It's not Labor who's chosen to define a small business tax cut as extending up to a billion dollars," Mr Shorten replied.
"The real cost of Malcolm Turnbull's big cash splash for business, the bulk of the return isn't for those businesses that you're talking about."
Treasurer Scott Morrison scoffed at that suggestion, saying Mr Shorten thought a business that had a turnover of just over $2 million was a multinational.
"He's out there lying to people, calling these businesses big banks, they are small family businesses," he said.
