Malcolm Turnbull's task of convincing wary state governments and Senate crossbenchers to back a GST increase has been made more difficult by new research showing it would have a severe impact on the least well-off but leave wealthier households unscathed.

Lifting the GST to 15 per cent would hit low-income households hard but its negative effects would go almost unnoticed by those at the top end of society, new modelling of the proposed changes has revealed.

The alternative idea of retaining the 10 per cent rate while broadening its base would be almost as regressive.

And offsetting the tax hike with lower marginal income tax would only make the disparity between rich and poor worse.

The analysis by the respected National Centre for Social and Economic Modelling shows the current 10 per cent GST consumes 13.4 per cent of disposable income for those in the bottom fifth of households, but that would rise to more than 20 per cent if the rate were lifted to 15 per cent, as is favoured by some within the Coalition government.

Households in the top 20 per cent, though, would experience a much milder impact, increasing from a mere 5.9 per cent of disposable income to 8.8 per cent.

Even just broadening the base to include fresh food, water and sewerage, health, and education would hit the poorest hardest, with the 13.4 per cent of disposable income jumping to nearly 18 per cent compared to a rise for the wealthiest from 5.9 per cent to 7.6 per cent.

The figures go a long way to explaining Labor's trenchant opposition to any GST increase and suggest that any compensation built in to ensure the poorest are left "no worse off" - as the Prime Minister has pledged - will require an enormous "churn".

But the Prime Minister's difficult policy challenge is not without its Labor backers. Three former Labor premiers, Kristina Keneally (NSW), Peter Beattie (Qld), and Geoff Gallop (WA) have told Fairfax Media they would support an increase to the GST subject to certain conditions including compensation for low-income earners, federation reform, and additional money for health and education.

While Mr Turnbull has determinedly kept all taxation options on the table while a white paper is being prepared, he is aware of the likely scare campaign coming his way if lifting the GST is part of the mix.

Girding for that fight, Mr Turnbull has repeatedly stressed that changes proposed would be built around the core Australian principle of fairness.

"Any changes to the tax system have got to be ones that ensure that there is no disadvantage to the most vulnerable Australians, to less well-off Australians," Mr Turnbull said this week.

"We are a very fair society in Australia and it is important that our tax system reflects that."

Cassandra Goldie from the Australian Council of Social Service, which commissioned the modelling, said ACOSS is not opposed to an increase in the GST but it should not be a "starting point" for tax reform given that it would hit low- and middle-income earners the hardest.

While some Labor figures back a higher GST in theory, federally the opposition is preparing a major anti-GST campaign and is likely to revive the words of the Tony Abbott in relation to the carbon tax, arguing an expanded or increased consumption tax would be profoundly damaging to household budgets, hit spending confidence, and ultimately would be a "great big new tax on everything".

Shadow treasurer Chris Bowen told the ABC's Radio National on Thursday morning the report "vindicates everything the Labor Party have been saying about the GST".

The modelling also shows if the GST was lifted to 15 per cent, and the extra revenue generated was used to fund a cut in personal income tax rates by 5 per cent, the overall progressivity of the tax system would be reduced much more than if the GST was raised alone.

In that scenario, the lowest 60 per cent of households would be worse off and the top 40 per cent would gain at their expense.

The lowest 20 per cent of households would lose $33 a week (worth 6.6 per cent of income) on average while the top 20 per cent would gain $69 a week (worth 2.1 per cent of income).

Dr Goldie said raising the GST to 15 per cent to fund personal income tax cuts would do nothing to ease pressure on state health, education and welfare budgets.

"If it's not about raising more revenue, the government has to justify why this option is being considered at all," she said.

The independent NATSEM modelling was commissioned by ACOSS, with support from the progressive-leaning Carnegie Foundation.

NATSEM's detailed modelling of the impact of the Abbott government's first budget led to the eventual conclusion of voters that its measures were harsh, unfair, and ideologically driven, contributing to its political failure.

Its assessment of the government's second budget showed much the same thing, that budget consolidation was being made at the expense of the less well-off, for the second year in a row.

With James Massola

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