In blistering evidence to a parliamentary inquiry examining the controversial proposal, Bruce Bonyhady said it was a disgrace that what he described as "robo-planning" hadn't already been abandoned.

Prof Bonyhady said the Morrison government was pursuing the changes to cut costs, an aim he said was born from an misunderstanding of what factors were putting the $22 billion scheme under financial pressure.

He also despaired at the fractured relationship between the disability community and the agency in charge of the scheme, saying distrust had plunged to a "new low".

Prof Bonyhady was the NDIS's inaugural chairman and led the panel which advised the Productivity Commission's work to design the scheme a decade ago.

Now the director of the Melbourne Disability Institute, Prof Bonyhady appeared before the inquiry on Friday morning to argue against changes he feared would undermine the purpose of the scheme.

The government's plan to use their own panel of contractors to conduct assessments on NDIS participants has faced fierce and sustained opposition from disability groups, Labor and the Greens.

New NDIS Linda Reynolds has bowed to pressure and paused the permanent rollout of independent assessments pending further consultation, but has made clear the government is committed to a system it believes will be fairer.

Prof Bonyhady cited a number of reasons as the basis for him being "totally opposed" to the new system.

He was highly critical of plans to use the same "toolkit" of standardised tests for assessments on participants, regardless of their disability.

He also raised alarm about the prospect that participants would have no avenue to appeal or challenge their assessors' findings in the Administrative Appeals Tribunal. The agency could use that power to cut participants' budgets or exclude people from the scheme, he feared.

"It is not just current participants and their families who should be anxious and angry about what the government and the NDIA have planned," he said.

"All Australians should be gravely concerned about robo-planning because it will tear up the social contract at the heart of the NDIS.

"This contract says that if you, or your child or grandchild is born with or acquires a significant or permanent disability then they will be eligible for tailored supports based on their individual goals and needs.

"This contract will disappear if robo-planning is introduced."

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Asked if the proposed changes could mark a turning point for the scheme, Prof Bonyhady went further.

"Robo-planning will blow up the NDIS," he said.

"It will also blow up the vision for this scheme to be there for all Australians."

Prof Bonyhady said he used the term "robo-planning" because of similarities to the controversial robo-debt program.

"Independent assessments are not independent, they are robo-planning and that is the term which I will use," he said.

"Every time you refer to the changes as independent assessments you are reinforcing a deliberate misrepresentation."

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