The Archbishop of Canterbury has backed criticism of the government's controversial welfare changes, warning they will have a "deeply disproportionate" effect on children.
Justin Welby has backed an open letter condemning the plans to change the benefits system.
In his first foray into politics since taking the post, he said politicians had a "clear choice" on whether to protect children from the effects of the benefit cap.
This is Justin Welby's first foray into political debate in his new role
The Archbishop of York, Dr John Sentamu, also backed the letter to the Sunday Telegraph.
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It comes as a blow to Iain Duncan Smith, the Work and Pensions Secretary, who is attempting to steer the reforms through Parliament.
Ministers claim benefit rises at 1% a year until 2016 are needed to help get spending "back under control" and create a fairer deal for taxpayers.
But the archbishop, who will be formally enthroned at Canterbury Cathedral on March 21, said the legislation would remove the protection given to families against the rising cost of living and could push 200,000 children into poverty.
He said: "As a civilised society, we have a duty to support those among us who are vulnerable and in need. When times are hard, that duty should be felt more than ever, not disappear or diminish.
"It is essential that we have a welfare system that responds to need and recognises the rising costs of food, fuel and housing.
"The current benefits system does that, by ensuring that the support struggling families receive rises with inflation.
"These changes will mean it is children and families who will pay the price for high inflation, rather than the Government."
He added: "Politicians have a clear choice. By protecting children from the effects of this Bill, they can help fulfil their commitment to end child poverty."
Welby's predecessor, Rowan Williams, regularly got involved in political debate, infuriating the government at times.
A spokeswoman for the Department for Work and Pensions said: "In difficult economic times we've protected the incomes of pensioners and disabled people, and most working age benefits will continue to increase 1%.
"This was a tough decision but it's one that will help keep the welfare bill sustainable in the longer term.
"By raising the personal allowance threshold, we've lifted two million people out of tax altogether, clearly benefiting people on a low income."