Documents released under freedom of information have revealed the agency's fears that it wouldn't be able to meet new service standards for participants without a funding boost in the coming years.

The review creates a longer-term headache for Labor, with figures showing the agency's operating budget - set by the former Morrison government - is not nearly keeping pace with the ballooning size of the scheme.

The Albanese government is boosting resources to the agency by abolishing the cap which restricted the hiring of permanent staff.

But the Greens are calling for a further injection of funds to the agency in the October budget, while the main public sector union said more was needed to turn around a "terrible situation" which it blames on the former regime.

The incoming government brief for NDIS Minister Bill Shorten has revealed the agency's concerns about its future funding levels, and the possible implications for the more than 500,000 disabled Australians who rely on the insurance scheme.

The brief shows that the Department of Social Services commissioned a review of the agency's resourcing last November.

The review, which was completed in March, found the NDIA's operating budget over the forward estimates was "inadequate" given the scheme's size and growth.

The brief showed that, as an "interim measure", the March federal budget increased the agency's funding for 2022-23 to $1.67 billion, matching the previous year.

But funding is set to fall over the next two years, with just $1.34 billion allocated for 2024-25.

That is despite the cost of the scheme forecast to skyrocket from $29 billion to $41 billion over the next three years, amid a projected surge in participant numbers from 530,000 to 670,400.

The agency warned Mr Shorten that its budget for this financial year was "not sufficient" to meet new service standards for participants, known as the Participant Services Guarantee.

"Without additional operating budget, the agency will not have the resources necessary to support the scheme and meet its obligations under the Participant Service Guarantee over the forward estimates period," the brief noted.

The brief revealed the agency and department were in the process of developing a proposal to "rebase" the NDIA's budget and staffing levels, which would be pitched to the Albanese government.

The agency is without a permanent chief executive and is searching for a new chair after Martin Hoffman and Denis Napthine resigned following the election.

The Canberra Times asked Mr Shorten if the government would increase the agency's budget in response to the review's findings.

Mr Shorten did not respond directly to the question, but said removing the staffing cap would amount to an increase in the resources.

"The removal of the staffing cap means more dedicated, more cost-effective permanent staff are working in the agency, to ensure participants are supported," he said.

READ MORE

The government plans to add 380 positions to the agency, according to the brief.

The Morrison government set the NDIA's staffing cap at 4500 this financial year. Another 1900 labour hire staff and another 5810 contractors were on the books as of June this year.

Greens disability spokesman Jordon Steele-John said Labor's commitment was a "drop in the ocean" compared to what was needed.

The Albanese government is tempering expectations ahead of its October budget, arguing it doesn't have much room to move because of the trillion dollars of debt it inherited from the Morrison government.

But Senator Steele-John said Labor could free up funding to invest in the agency by scrapping planned tax cuts for high-income earners.

"I think this is an opportunity for the government to demonstrate to the disability community that they have heard what we have told them at the election," he told The Canberra Times.

"What the disabled community told the government, told every political party, was stop treating us like a punching bag, or a cash cow and sit down and authentically engage with us."

The union which represents NDIA workers welcomed Labor's commitment to increase permanent staff numbers, having for years called for an increase to the agency's funding.

But Community and Public Sector Union national deputy secretary Beth Vincent-Pietsch said more investment was needed, including for the NDIS quality and safety regulator.

"The NDIS has been run down by the former Morrison government, and it is our most vulnerable people with disabilities who paid the price," she said.

"The CPSU welcomes a fresh approach but recognise much needs to be done to turn this terrible situation around."