The budget, which Treasurer Josh Frydenberg handed down on Tuesday night, contains an additional $13.2 billion over four years for the NDIS. It comes after the federal government provided a further $3.9 billion for the scheme in the previous budget.

In an interview earlier this month, Linda Reynolds, the newly minted Minister for the NDIS, foreshadowed "hard discussions" about the sustainability of the scheme's current funding model, with the budget forecasting it will cost the Commonwealth more than $30 billion by 2024-25.

However, National Disability Services, Australia's peak industry body for disability service organisations, has highlighted that this figure shouldn't have come as a shock, given it was effectively forecast in a 2017 Productivity Commission report.

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Launceston-based disability consultant Jane Wardlaw said the idea that there was an "over-spend" on the NDIS was "an absolute furphy".

"Fundamentally, what is wrong with the design of the scheme is it has not been implemented in the way that it was designed to be built," Ms Wardlaw said. "And the scheme itself was meant to be a three-tiered system. Because, when all is said and done, the capacity-building component of the NDIS has not been invested into or built the way it should have been."

"So I think it's inevitable that we will see some type of cost-cutting and cost-controlling measures. I think we need to resign ourselves to that fact.

"I welcome the budget, personally. I welcome the idea, from a glance, that there has been some investment into some mainstream services like mental health and so forth. But I want those organisations to lift their game about being better service providers to people with disability."

NDS chief executive David Moody said politicians needed to "drop the politics" when discussing the NDIS and forego "media headline comparisons to Medicare".

"At the moment we are hearing scary talk about a scheme in danger, which is unsettling for people with disability, and inconsistent with the Productivity Commission's outlook from 2017," Mr Moody said.

"Our ask now is that the government and [National Disability Insurance Agency] commit to constructive conversations with NDS, our members, and other disability sector stakeholders to help develop solutions to any concerns the NDIA or minister has."

After taking on the NDIS portfolio in March, Ms Reynolds put a halt to plans to roll out independent assessments for the scheme by the middle of the year, a prospect that had alarmed advocates.

About 450,000 Australians are participants in the NDIS, with that number having grown from a trial of about 7000 in 2013-14.