Former Liberal treasurer Peter Costello has weighed into the tax reform debate, saying the Turnbull government still hasn't identified the problem it is trying to fix.
Treasurer Scott Morrison insists everything remains on the table, saying the government has moved on from eight years of "rule-in, rule-out, gotcha politics".
"All of that sort of thing basically euthanised public policy debate in this country," Mr Morrison told Sky News on Sunday.
His comments came as the Greens pointed to new Parliament Library analysis showing a carbon tax would raise as much revenue as increasing the GST rate or broadening its base, while having less impact on households.
Greens MP Adam Bandt said if everything were on the table, then the original carbon tax should be re-considered.
"That is fairer and it will help cut pollution," he said in Canberra on Sunday.
Mr Costello said everyone was out there saying Australia doesn't raise enough tax.
"What is the government's position? What does it say is the problem? I don't think we're even now at the stage of getting to the solutions," Mr Costello told Network Ten on Sunday.
Former Labor NSW treasurer Michael Costa told Ten the debate was confused and had gone "off the rails".
But Mr Morrison reiterated that Australia does not have a revenue problem that would require people to be taxed more.
"Our problem at the moment is Australians aren't earning enough, not that they are not paying enough tax," he said.
Finance Minister Mathias Cormann agreed the government was looking to improve the tax mix, not increase the burden on taxpayers.
He said if the tax mix were improved, and the system was more efficient and less distorting, it would encourage people to work more, save more and invest more.
"Then the stronger growth will deliver a dividend to government which, of course, can be then invested in the important benefits and services provided by government," Senator Cormann told Ten.
But opposition finance spokesman Tony Burke said if the government wanted to be fair, it would not expand the GST.
"Every change the government is contemplating on the GST has the same thing in common - it hits hardest the people who can afford it least," Mr Burke said in Sydney.
Mr Morrison said Australians won't cop changes to the tax system that just end up giving the states a "bucket of money" to spend as they are now.
But Victorian Premier Daniel Andrews said what Victorians won't accept is more cuts to hospitals and schools.
"I reckon people are starting to get pretty sick and tired of Liberal governments whose only answer to everything is to cut spending on the things that matter most and jack up taxes," he told reporters in Melbourne.