Social Security Minister Hugh Bayley is facing a backbench revolt of Labour MPs angry at radical welfare reforms.
It is the York MP's biggest ministerial challenge in the Commons so far.
At least 20 MPs are backing amendments to the Government's flagship Welfare Reform Bill.
The get-tough new laws emphasise that claimants have "responsibilities as well as rights."
But the backbench MPs are against making Incapacity Benefit "means-tested" for people who have saved for their retirement.
They are also opposed to changes which would deny this benefit for people who have not paid enough National Insurance in the last two years.
Long-time campaigner for the disabled, Roger Berry MP, says he has the support of up to 100 MPs for the amendments.
But junior minister Mr Bayley, who is playing a key role in bringing in the new laws, defended the Labour Government's reforms.
He said: "The Government is providing more support for the poorest and most severely disabled people who have no hope of getting a job. Incapacity Benefit was always intended to replace earnings for people forced to give up work because of disability or ill-health - and not for the long-term unemployed.
"We are spending £225million on creating job opportunities for disabled people who want to work."
He denied Incapacity Benefit was being means-tested. Claimants who receive more than £50 a week from a private pension or health insurance would only get 50p for every pound of Incapacity Benefit.
But Mr Bayley said the benefit would only be totally phased out for people receiving about £200 a week.
Otherwise claimants who had retired would be receiving more than those still working.
He stressed the Government was restoring the link between paying NI and receiving Incapacity Benefit. But he added people, like the long-term unemployed, who had not paid NI in the last two years could still benefit from the Severe Disabled Premium on Income Support.
Lilian Parkinson, co-ordinator of York's Disability Rights and Resource Centre, said she had already met with Hugh Bayley to put across their concerns with the Bill.
"We're not happy with some of the changes being proposed," she said.
She predicted one of the biggest groups to suffer would be disabled women with partners.
"At the moment women who may not have paid enough National Insurance contributions to qualify for Incapacity Benefit can claim Severe Disablement Allowance.
"But the Bill is phasing the allowance out and these people will not get anything."
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