Prime Minister Turnbull said he has yet to be convinced that a GST increase would be a good thing, but added that discussions would continue.
"It's not a question of politics here," he said on ABC Insiders. "At this stage, I remain to be convinced or persuaded that a tax mix switch of that kind would actually give us the economic benefit that you'd want in order to such a big thing."
He said changing the GST is complex and would need careful consideration from all angles.
"You have to first decide: is this policy going to give you the economic outcome you want? Then you have to assess the practical politics. With the GST income tax swap proposal, it has not yet passed that first test and that's what the analysis is being undertaken," he said.
Prime Minister Malcolm Turnbull last week appeared to cast doubt that his government would go ahead with a change in the GST as part of its tax reform package.
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Keep calm about GST debate: Joyce
A senior Liberal senator says he won't support increasing the GST to 15 per cent.
Senator Ian Macdonald says he's one of the few members of parliament who was around when the 10 per cent GST was introduced in 2000.
Senator Macdonald has told ABC television the main reason for his opposition is that politicians gave a "rolled-gold commitment" at the time that they wouldn't be part of any increase beyond 10 per cent.
Cabinet Secretary Arthur Sinodinos is saying "nothing is inevitable".
"I think it is correct to say that he hasn't been persuaded that the GST is some sort of silver bullet," Senator Sinodinos told Sky News on Sunday.
But he said the debate over tax reform can't run too much longer.
"Clearly there has been a lot of discussion out there. The next stage people want to see the colour of our money, or the colour of their money, in a way we want to play with it," he said.
