Thousands of cancer patients could lose benefits under government proposals, a charity has warned.
Macmillan Cancer Support is attacking plans in the Welfare Reform Bill to remove the Employment and Support Allowance (ESA) after a year.
It estimates 7,000 people could be affected - and could lose up to £94 a week, even if they are not ready to return to work.
The government said people receiving treatment would not be affected.
The Welfare Reform Bill enters the report stage in the House of Commons on Monday.
ESA claimants are divided into two categories - those undergoing treatment are in the "support group" and there is no time-limit.
But those who are deemed able to perform "work-related activities" which might help them eventually return to work face means-testing after 12 months.
Anyone with savings of over £16,000, or whose partner either works more than 24 hours or earns more than £149 a week would lose all their ESA.
Macmillan wants the bill amended so everyone who is eligible for ESA will receive it for as long as they need it, regardless of their financial circumstances.
Ciaran Devane, chief executive of the charity, said: "Many cancer patients will lose this crucial benefit simply because they have not recovered quickly enough.
"The majority want to return to work as it can represent a milestone in their recovery and a return to normality, in addition to the obvious financial benefits."
He added: "This proposal in the Welfare Reform Bill will have a devastating impact on many cancer patients."
Professor Jane Maher, Macmillan's chief medical officer added: "In my experience one year is simply not long enough for many people to recover from cancer.
"The serious physical and psychological side-effects of cancer can last for many months, even years, after treatment has finished.
"It is crucial that patients are not forced to return to work before they are ready."
A spokeswoman for the Department for Work and Pensions said: "We are working closely with Macmillan to ensure that people with cancer get all the support from us they need.
"Those who are severely ill and are in the support group of ESA will see no change to their benefit entitlement. Nor will there be any change for those on income-related ESA."
She added: "We have recently amended legislation so that individuals awaiting or between courses of certain types of chemotherapy will automatically be placed in the support group."