Caritas Social Action Network claims two hundred thousand children will be pushed further into poverty by a cap on benefits beginning to be rolled out today.
Couples and single parents living in four London boroughs - Croydon, Bromley, Haringey and Enfield - will receive no more than £500 a week.
The limit's being brought in to bring benefits into line with average income and will be rolled out across England, Scotland and Wales from July.
Liam Allmark from CSAN (Caritas Social Action Network), the social action arm of the Catholic Church in England and Wales, told Premier's Victoria Laurence on the News Hour it hasn't been properly thought out:
The government last week claimed the number of people expected to be hit by the cap had fallen from 56,000 to 40,000, with eight thousand claimants finding work through JobCentre Plus.
Christian Guy from the Centre for Social Justice thinktank believes state handouts can harm people's career prospects.
He said:
"For a long time the welfare system has trapped people in low income in poverty because they've been able to earn vast sums of money, more than they would earn in work, and so this is about saying you are better off in work."
Earlier today on Twitter, Prime Minister David Cameron said it was a' big day for welfare reform. Amazingly Labour oppose it'.
But The Children's Society is also criticising the plans. In a statement its Chief Executive Matthew Reed said:
"This is a blunt instrument trying to solve a complex problem.
"The policy may be targeted at workless adults, but in reality children are seven times more likely than adults to lose out.
"We estimate that 140,000 children, compared to 60,000 adults, will pay the price as parents have less to spend on food, clothing and rent.
"Families, especially in London where the cap is being launched, may have their lives disrupted as they are forced to find cheaper rents in other parts of the country, resulting in children having to leave their schools and friends and vital support networks broken.
"The cap will also put pressure on public services in the communities where they are forced to relocate.
"We fully support efforts to make work pay. But it is not right to achieve this by putting more children on the breadline.
"The government must review the full impact of this latest measure on children and families before it is rolled-out across the country."
People on disability benefits will be exempt from the cap and to encourage people to seek work, ministers have decided that people with a job who receive Working Tax Credit will also not be affected.
Ministers claim that the threat of the introduction of the cap has already spurred 8,000 claimants who would have lost out to find jobs.
Elsewhere, unions have reacted to the latest rise in the minimum wage saying it's not enough.
Adults will see an increase of 12 pence an hour in October to £6.31p
But the GMB has said it's well below inflation, while the Unite union wants a rise of a pound an hour.
The increase is five pence for those between 18 and 20, while apprentices get an extra three pence an hour.