Birmingham MPs have been urged to back plans to cut benefits for hundreds of their constituents in a personal plea from the Cabinet Minister in charge of the reforms.
Clare Short (Lab Ladywood), Roger Godsiff (Lab Sparkbrook & Small Heath) and Sion Simon (Lab Erdington) have received letters from Work and Pensions Secretary John Hutton.
The Birmingham constituencies are among the top 100 in the country for the number of people claiming incapacity benefit.
In some Birmingham wards, more than a quarter of the working-age population receives the benefit.
Tony Blair has promised "radical" changes to the system, which allows 2.7 million people to claim £12 billion a year.
Measures could include imposing a time limit on eligibility, or giving claimants vouchers instead of cash, which can only be exchanged for money by taking part in a training programme.
But Ministers face a tough fight to convince Labour backbenchers to support the proposals.
There are 7,600 people claiming incapacity benefit in the Ladywood constituency and 7,500 in Sparkbrook & Small Heath.
Another 6,400 people are claiming incapacity benefit in Erdington.
In his letter, Mr Hutton told the MPs: "I do not believe we should accept a system that perpetuates hardship and denies people the opportunity to better their lives by accessing the world of work.
"The vast majority of people who start receiving incapacity benefit want to go back into work, but the system currently provides them with little help in doing so."
Incapacity benefit is paid at a rate of £57.65 a week for new claimants. In many cases that rises to £68.20 after six months and £76.45 after a year.
Erdington MP Sion Simon said he backed the reforms.
"In the Erdington ward in my constituency, 26 per cent of the working-age population is on incapacity benefit.
"It clearly cannot be correct that more than a quarter of people are unfit to work."
The list of 100 constituencies also includes Sedgefield, near Newcastle - where the MP is Tony Blair, and 6,600 people claim incapacity benefit.
Ministers say the existing system invites abuse by encouraging people to stay off work to keep claiming the maximum payment.
Mr Hutton said: "In households where nobody goes to work, both money and self esteem can be in short supply.
"This can mean a lack of positive role models and result in generation after generation getting stuck in the benefits trap.
"Getting people on to incapacity benefit - and its predecessors invalidity benefit and sickness benefit - was seen as a way to mask soaring levels of unemployment."
Reports that the reforms were to be scaled back because of a lack of backbench support were denied by Downing Street last month.
Mr Blair already faces a tough fight with many in his own party over school and health reforms.