The Federal Government is contemplating halving the capital gains tax discount for superannuation funds, in its quest to find money to fund income tax cuts.

Key points: Government mulls halving super fund capital gains tax from 33 per cent to 15 per cent

Government mulls halving super fund capital gains tax from 33 per cent to 15 per cent Finance Minister refuses to confirm the proposal

Finance Minister refuses to confirm the proposal Industry Super Australia warns cuts could increase speculative short term investment

If it does, it would appear to be at odds with the Prime Minister's bold declaration to Parliament that: "Increasing capital gains tax is no part of our thinking whatsoever."

Malcolm Turnbull made the statement in a swingeing attack on Labor's policies to limit tax deductions on investment properties to new homes and to halve the capital gains tax discount on assets held for more than a year from 50 per cent to 25 per cent.

On capital gains, Mr Turnbull said the change would hammer investors because the tax on their real gain after inflation would be 70 per cent.

"Nothing could be more calculated to put the brakes on investment, jobs and growth," he said.

But when questioned about the statement the Prime Minister's office said he was only ruling out the tax options proposed by Labor, which focus on property.

What are capital gains? Capital gains are the profits that a fund, or an individual, makes on the sale of an asset. Capital gains tax is imposed on those profits. Currently, superannuation funds are given a 33 per cent discount on the tax they need to pay on the profits they make on the sale of an asset (as long as it is held for more than 12 months). The Prime Minister is now looking to halve that, meaning while the tax rate remains the same, the discount given would fall to 15 per cent.

Finance Minister Mathias Cormann refused to confirm the proposal when asked by the ABC.

"It's a matter of public record that we have been looking right across the whole of the tax system to assess opportunities for improvements," he said.

"The announcements, the specific announcements will of course be made when we have finished that work. I'm not going to add to the speculation."

How can we take Turnbull seriously? Opposition hits back

Shadow treasurer Chris Bowen said the Government could not be trusted on tax reform if the Prime Minister said one thing in the afternoon and his staff said something different hours later.

Mr Bowen said Mr Turnbull's character should be questioned over the turnaround.

"He cannot be trusted on tax," he said.

"If he can't be trusted on something he says at Question Time at 2:00pm, how can his commitments about the GST be taken seriously?

"How can his commitments about any other matter of tax be taken seriously?"

Matthew Linden from the super fund Industry Super Australia warned against a halving of the capital gains tax discount for superannuation funds.

"It could give rise to an increase in speculative short term investment and that would be a bad thing for members," he said.

The ABC has confirmed the Government is considering halving the super fund capital gains tax concession from 33 per cent to 15 per cent.

Chris Richardson from Deloitte Access Economics said the move would not be a big money spinner for the Government.

"We're now in a world where some of the bigger options in tax reform have been ruled out," he said.

"The GST initially and Prime Minister now moving to hose down speculation in some other areas as well, that may mean that the Government is on the hunt for some small buckets of savings."