A leading accounting group has savaged Federal Treasurer Joe Hockey's comments on income tax cuts, accusing him of repeating rhetoric instead of fixing Australia's "broken down tax system".

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Mr Hockey made the case for income tax cuts, including for Australia's highest earners, during a speech in Sydney in which he highlighted the problem of "bracket creep".

He said the Government had to cut taxes for middle and low-income earners, saying that without the changes, almost half of all taxpayers would be in the top two tax brackets in a decade.

But Certified Practicing Accountants (CPA) Australia's Alex Malley has lashed the Government for what he called pre-election "fiscal giveaways".

"The Treasurer appears to be caught in a cycle of restating the problems rather than rethinking the solutions," Mr Malley said.

"The issue of income tax, GST, super [annuation], company tax, land tax is yet to be discussed ... it really is being deferred and deferred and deferred.

"To actually start forcing a conversation around just personal income tax says to me that we're in a downhill slide to an election and that's not good for Australia, we need to make some tough decisions.

"To defer and distract again in relation to tax and tell us what we already knew at a five-star hotel in Sydney is not my idea of leadership."

The Treasurer argued the tax changes would help economic growth.

"If people are left in those higher tax brackets ... the incentive for hard work is blunted — and inflation means that without a real wage rise, people pay a higher and higher average tax rate each year," he said.

"If people are discouraged from work and we cannot address our workforce participation challenges, then Australia will face greater economic pressures," Mr Hockey said.

"The price we pay for failing to strengthen and improve our tax system is less income than Australians should receive and fewer jobs than Australians could hold.

Asked on 612 ABC Brisbane whether income tax cuts or returning to surplus was his priority, Mr Hockey replied: "Well, it's both."

"We illustrated that in our May budget, where we were able to give small business a $5 billion tax cut. We were able to do that by finding [and] offsetting savings.

"It is hugely important that we have targeted tax cuts that help grow the economy ... which in turn helps to create greater wealth and then gives us more revenue."

Labor labels Hockey speech 'thought bubble'

Mr Hockey said Australia's highest marginal tax rate — at 47 per-cent — is higher than countries including New Zealand and Singapore.

He was expected to argue the top rate kicks in earlier than other countries, and the tax system relies too much on high income earners.

Shadow treasurer Chris Bowen said Mr Hockey brought no credibility to a discussion about tax changes.

"This is more talk from the man who's been talking about lower and fairer taxes for several years now and has delivered higher and more unfair taxes, and especially unfair spending cuts," Mr Bowen said.

"The billions of dollars of cuts that would be necessary to fund the sort of tax cuts that Joe Hockey's flagging today would come at a very significant cost.

"Joe Hockey needs to outline in much greater detail than he has in a thought bubble today, how he's going to go about this plan."

Respected economist Saul Eslake said bracket creep was an issue that needed to be addressed, but that reducing the overall tax take was hard to justify.

"While there is a good case for doing something about the likelihood, the certainty, that people will be pushed into the second top tax bracket who shouldn't be there, there is also a compelling case ... for other reforms to the tax system that will help keep the budget on a sustainable footing, as there is also a case, of course, for continued restraint in government spending," he said.