Health Minister Mark Butler will on Wednesday outline reforms to the $50 billion scheme, which are likely to include changes to who is eligible for support and tougher registration requirements for providers.
But as the government declared it would be negligent to allow NDIS expenditure to continue growing at about 10 per cent a year, people with disabilities and advocates warn cuts to services would leave participants worse off.
Prime Minister Anthony Albanese said the scheme needed to carry out its original function to provide support to those with serious disabilities.
"What's important is that it be made sustainable, because it's too important to be undermined in terms of confidence in the scheme," he told reporters in Sydney.
"What we want to do, though, is to make sure that Australians with disability, who the NDIS was aimed at, continue to receive really important support so they can fully participate in society."
Greens disability spokesman Jordon Steele-John said the community was worried NDIS reforms would not result in positive changes for those receiving support.
"Disabled people and their families are sick of being used as political footballs," he told ABC Radio.
"We're in a situation right now where the government is saying we cost too much.
"People cannot understand ... why a government facing a budget, which is ultimately always about choices, would choose to cut their services."
People With Disability Australia president Jeramy Hope said the government needed to focus on making the scheme more efficient by reducing bureaucracy, rather than cutting eligibility to save money.
"Our community is scared and we want a surety that things are going to be OK," he told AAP.
Changes announced in August will involve some children with autism being moved off the NDIS and into a separate program called Thriving Kids.
That program will begin rolling out from October and be fully implemented by January 2028.
On Tuesday, Mr Butler and Treasurer Jim Chalmers briefed state and territory officials, who are reluctant to agree to any changes that would require them to pay more.
Queensland Premier David Crisafulli said he expected states and territories to push back against calls from the federal government for jurisdictions to do more of the heavy lifting.
"I want the federal government to deal with the system, deal with the rorters, but make sure that every single person who deserves support, deserves compassion, gets it," he said.
"You're going to see a chorus of states and territories from different sides of the political fence, and I've got a feeling most of them are going to be saying something very, very similar."
Martin Laverty, one of the architects of the NDIS, said the scheme was not designed to meet the needs of everyone with a disability.
"It was designed, sadly, for those with the most significant, permanent and profound disabilities, and because other disability programs ceased, the NDIS was overwhelmed," he said.
"Now it's the chance to reset and to establish evidence-based programs for people with mild to moderate disability outside of the NDIS itself."
