Reining in spending on the National Disability Insurance Scheme will be the centrepiece of a savings package Treasurer Jim Chalmers is preparing for the May budget.

As the impact of the Iran war continues to hit Australia’s economy, Chalmers has lowered expectations for how much the government’s bottom line will be improved in the fiscal update.

With oil prices again rising after more uncertainty around the Strait of Hormuz, he acknowledged the consequences to Australia’s economy, including unemployment, could become severe.

Chalmers conceded on Monday that a savings package the government was preparing would be different to what was planned before the Iran war. He also said economists’ predictions for a big boost to tax revenue as a result of the conflict were overblown.

“If we take the impacts of this war in the Middle East on the revenue side, it’s possible, if we were finalising those forecasts today, that in some years the revenue impacts would be negative rather than positive,” he said.

Independent economist Chris Richardson had previously estimated higher commodity prices and income tax revenue, partly due to the war, would yield a $30 billion increase in the tax take over the next four years.

Still, the government was planning substantial savings to get the budget back in shape, Chalmers said.

The NDIS would be “easily the most important part” of the savings package, he said.

The government aims to reduce annual growth in the $52 billion a year scheme from more than 10 per cent to 5-6 per cent.

NDIS Minister Mark Butler will speak at the National Press Club on Wednesday, when he is expected to focus on unregistered providers as well as how support packages are priced.

HSBC chief economist Paul Bloxham said it was important higher spending in the budget did not exacerbate inflation and force the Reserve Bank to lift interest rates higher than it otherwise would.

Labor has already pledged billions in cost-of-living support, such as cuts to the fuel excise, and “economic resilience” measures, such as underwriting fuel cargoes.

Supply-side reforms that boosted productivity should remain the focus, Bloxham said.

To lift productivity and lower costs, a group of peak bodies led by the Business Council of Australia called for a stocktake of regulations, an overhaul of planning rules and strategies to boost research and development in the budget.

Recent research from the Australian Institute of Company Directors and consulting firm Mandala found firms were spending almost $160 billion a year to comply with federal laws.

“That kind of red tape adds cost, slows things down and makes it harder to keep goods moving and shelves stocked,” Business Council chief executive Bran Black said.

Finance Minister Katy Gallagher said the budget would include some regulatory reform.

National Farmers Federation chief executive Mike Guerin said changes to recently introduced national environmental laws could make an immediate difference to supermarket prices.

While businesses want less regulation, more than 50 advocacy groups are want reforms such as a 25 per cent levy on exported natural gas – a measure fiercely opposed by the resources sector.

It would raise up to $17 billion every year, allowing the government to spend more on housing, energy efficiency upgrades and support payments including JobSeeker, the coalition of organisations said.

They also want the capital gains tax discount for investment properties reduced by half and negative gearing phased out over five years.

Labor is widely tipped to pare back incentives for property investors in the budget.

Asked about reports the government was planning to revert the capital gains tax discount back to the pre-1999 regime, which pegged the discount to inflation rather than a flat 50 per cent, Chalmers said there was more work to do on tax reform options in the budget.

“We have been really up front for some time now in saying that we do think that there is intergenerational unfairness in the tax system,” he said.

“The housing market is where some of those intergenerational issues are most obvious.”

-with AAP