Prime Minister Tony Blair has outlined plans for getting more people off incapacity benefit and into work.
Everybody who can work should be helped to do so, says Mr Blair
The government is due to unveil its five-year plan for welfare reform later this week.
Mr Blair, speaking in Manchester, said: "Those who play by the rules get the help, those who don't play by the rules should start playing by the rules."
Tory shadow work and pensions secretary David Willetts says the proposals will not work in reality.
Changes to incapacity benefit prompted rebellion from 65 Labour MPs in 1999 but the government says there is a strong case for reform.
Mr Blair said there would be three "key elements" to plans for new claimants for incapacity benefit (IB).
These would include reforming rules which pay claimants more the longer they are on benefit and penalise those who want to return to work.
He promised more support for the most severely sick and disabled, and encouragement for claimants who engaged in rehabilitation, training and work preparation.
Nobody would be "written off", he said, but everyone was expected to "fulfil their responsibilities" to work if able to do so.
Mr Blair said: "People are prepared to pay the money that is necessary to go into investment provided they think the system they are operating under is fair."
His aim was a system which rewarded work and learning and targeted abuse.
More than one million people on incapacity benefit wanted to work, claimed Mr Blair.
The details of the reform will be fleshed out on Wednesday and ministers have hinted the name "incapacity benefit" could be changed.
For the Tories, Mr Willetts said the plan was aimed at winning headlines, not getting people back to work.
"It is classic Blairism - it sounds tough, it will generate a row, the left-wingers will say it's appalling, but in the real world, it won't help," he said.
The Tories say they could help 250,000 Incapacity Benefit claimants over four years by using the voluntary and private sectors to provide a personalised service to get people back into sustained jobs.
Steve Webb, Liberal Democrat work and pensions spokesman, said Labour had "failed to get to grips with this issue".
He urged Mr Blair to adopt his party's plans for a new partial capability benefit to allow people to undertake varying amounts of paid work without becoming ineligible for some level of benefit.
"We need a system that fits people rather than the other way around," he said.
The government has ruled out reducing the starting £55-a-week rate for incapacity benefit or imposing a time-limit on the period for which the benefit can be claimed.
But it is thought ministers could remove automatic increases after six months or a year.
Former Labour Welfare Reform Minister Frank Field said unemployment benefit and incapacity benefit should be paid at the same rate.
That would remove incentives to move between the two - something the government has hinted it is considering.
Jon Knight, from disability charity Leonard Cheshire, has warned the government plans could make disabled people even poorer.
"People whose condition causes them pain or fatigue should not be forced to look for employment," he said.