A Cambridgeshire disability charity has said new tests to find out who is entitled to benefits are not working.
Rules to tighten up who is entitled to disability benefits and who should instead receive Jobseeker's Allowance were brought in by the Labour government and are being backed by the new coalition.
Support groups argue vulnerable people are losing out on vital payments as more claimants lose £30 a week after being assessed as able to work and put onto Jobseeker's Allowance.
Under the new system, claimants fill out a lengthy questionnaire about their health, then undergo a 45 minute medical exam.
Critics say the tests are flawed.
Andrew Gardner, of the Headway Brain Injuries charity, told the BBC Politics Show in the East: "Removing someone's benefit just like that after a 45-minute assessment is not about empowering people.
"The worst thing that can happen is someone goes back to work before they're ready - they're there for a month or a couple of weeks. But they can't really do the job, so they're sacked or they leave for whatever reason, and then they're just in a downward spiral again."
Matthew Lester, the director of Cambridgeshire employment and rehabilitation charity Papworth Trust, said: "Our concerns are that the assessment isn't working. We want proper resources for those in need.
"The assessment doesn't seem to work and to determine fitness for work with a broken test is wrong."
Employment minister Chris Grayling said: "I want the system as perfect as we can possibly get it.
"I don't want people to appeal and demonstrate the decision in the first place was wrong.
"So I want a system that is fair and thoughtful and that explains to people it is not simply a pass or fail, it is about whether they can do something better with their lives, whether we can help them back into employment.
"What I'm not prepared to do is write off a particular group because everyone is different.
"There are no financial targets to hit to force people back into work, this is about doing the right thing for people."
The Politics Show report will be broadcast on BBC One in the East at 1200 GMT on Sunday.