The Turnbull government will use savings from the National Disability Insurance Scheme to help pay for its contribution to it in future years.
Social Services minister Christian Porter introduced a bill on Tuesday to create a savings fund to pay for the federal government's contribution to the scheme after 2019, when it says it faces a $5 billion funding shortfall.
Mr Porter said the fund would have an opening balance of $162.4 million in NDIS savings, set aside last year after trials revealed that "some future costs during transition will be lower than originally anticipated."
If passed, the fund would allow the government to "pool and protect underspends and specific savings from across government over future years, locking them in as forward contributions to the NDIS," he said.
Mr Porter said it would also ensure savings were not returned to consolidated revenue "and effectively lost for NDIS purposes."
A spokesman said that savings across government, and not from the scheme, would make up most of the fund.
It is understood the bill came as a surprise to the NDIS board and disability advocates.
People with Disabilities Australia spokesman Craig Wallace questioned why NDIS savings were being put into a federally-controlled fund, rather than being spent on urgently needed disability services, including information services, guide dogs and technical aids.
Shadow disability reform spokeswoman Jenny Macklin has denied the government faces a shortfall, saying Labor had identified how the NDIS would be funded for a decade, through measures including an increase in the Medicare Levy.