Disability services group CCS says it has "grave concerns" about plans to introduce work ability assessments, influenced by controversial tests conducted in Britain.
From July, the invalid's benefit, paid to about 85,000 New Zealanders, will be replaced by the supported living payment, as part of wide-ranging welfare changes.
Social Development Minister Paula Bennett has said this would mean little change, although in a speech to health professionals late last year she signalled a new assessment regime which "echoes" the British process.
Measuring the extent to which disabled can work, the British tests have prompted a debate in the British Parliament, as well as protests targeting the Paralympics where Atos, the private company doing the tests, was a sponsor.
CCS Disability Action chief executive David Matthews cited research showing the British Government had spent £42.2 million (NZ$80.5m) on appeals against the tests, about 40 per cent of which overturned Atos' findings.
The tests were developed partially on the work of disability expert Professor Sir Mansel Aylward, who has visited New Zealand to advise on health reform, meeting Mrs Bennett.
Mr Matthews said most Government policy focused on how society builds barriers for the disabled, whereas a key part of Prof Aylward's work focused on the extent to which a disabled person could overcome barriers.
"The whole philosophy and approach to disability in New Zealand is based on the social model . . . which looks at the barriers to employing people, rather than what's wrong with the individual," he said. "We have grave concerns about basing welfare changes in New Zealand on such a flawed approach."
A work ability test would be an extra requirement for the disabled.
Mrs Bennett's spokeswoman said details of the assessments were being considered by a select committee and had not been finalised.