Health advocates have called for a Medicare-style levy to be introduced to secure funding for the National Disability Insurance Scheme.
Disability Support Service founder Michael Metcalfe said the scheme's hundreds of thousands of participants need consistent funding.
"Rather than risk further future cost pressures on the NDIS amidst economic peaks and valleys, revisiting a Medicare-style levy would offer greater certainty for all Australians," he said.
Disability groups have arrived in Canberra to present an open letter to parliament on budget day, to kick off a month-long campaign against "cruel" and "unexplained plan cuts".
The letter will detail the hardships felt by people who have had their funding reduced.
It comes as modelling released by industry group National Disability Services on Tuesday shows a $2.25 return for every dollar spent on the NDIS.
The scheme contributed about $52.4 billion to the Australian economy in 2020/21, according to the research.
The report found the NDIS employed more than 270,000 people, in more than 20 different roles.
About 500,000 people living with a disability rely on the NDIS.
Every Australian Counts campaign spokeswoman Elly Desmarchelier said people relying on funding were being left without basic support to live with dignity.
"We are getting reports every day from all over Australia from people who are not getting the individualised funding they need to live with dignity - it's cruel and dehumanising," she said.
"The NDIS is falling so far short of its promise that, for people with disability, it feels like it was a lie."
The Defend our NDIS campaign will head to marginal seats and regional towns during the federal election.
National Disability Services chief executive Laurie Leigh said the NDIS supported the nation's economy and employed a large number of women.
"It's disappointing that the focus over the past 18 months has changed from the benefits of the scheme to the cost, with repeated attempts to restrict access to the NDIS and reduce supports available," Ms Leigh said.
"Disability organisations and their workforce helped campaign to secure the NDIS and will continue to stand alongside people with disability to ensure the scheme is one that puts people first."
Full details of NDIS funding will be outlined in the budget.
