Secret documents obtained and published online by The Guardian show the National Disability Insurance Agency has established a "Sustainability Action Taskforce", which has been charged with making "immediate changes" to rein in costs.

While the memo states the taskforce is not linked to the government's highly contentious NDIS overhaul, the revelations will fuel concerns the Morrison government is intent on cutting costs.

The internal memo, marked sensitive and not for external distribution, said the taskforce had been set up to identify and deliver the actions needed to avoid a forecast budget blowout in 2021-22.

It said the total budget for participants was growing an average 23 per cent per year between 2019-20 and 2021-22.

That was about six times higher than the capped level.

The memo said costs were rising at a rate much higher than expected because it had been building participant budgets based on "inconsistent information and decision-making".

"The actions of the the SAT will make immediate changes to slow growth in participant numbers, slow growth in spend per participant and strengthen organisational discipline, in accordance with the NDIS Act and Rules," the document said.

"The work of the SAT is to do our statutory job to run the scheme on a sustainable trajectory. We need to act now to ensure we can deliver a better NDIS."

The revelations about the new taskforce, first reported in The Saturday Paper, have sparked an immediate backlash.

Labor urged new NDIS Minister Linda Reynolds to call off the "disability razor gang".

"After nearly eight years of Liberal governments, the documents reveal a knee-jerk plan to slash costs because those in charge have bungled the books," Labor's Bill Shorten and Kimberley Kitching said in a statement.

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Greens disability spokesman Jordon Steele-John said the disability community had for years called out the federal government for attempting to "cut corners" with the scheme.

"Now we've got the proof that this has been their intention all along," he said.

"We should not be having to fight the system that was created to support us. Any change to the way that NDIS participants are assessed, or to the scheme itself, must be co-designed with disabled people, our advocates and our peak bodies."

In a statement, Senator Reynolds' spokesman said the scheme was "demand-driven and fully funded". He said a further $3.9 billion had been budgeted over the forward estimates to reflect growing demand.

"The minister is committed to working collaboratively with states and territories and the sector to ensure the NDIS achieves the coverage intended and supports quality outcomes for all NDIS participants in a way that is fair, equitable, consistent and affordable," he said.

"The government also acknowledges its responsibility to ensure that participants continue to receive the reasonable and necessary supports they need, and to ensure the long-term financial endurance of the scheme."

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