The Welfare Benefits Up-rating Bill will cap benefit rises at 1% a year until 2016.
Work and Pensions Secretary Iain Duncan Smith, who is attempting to steer the reforms through Parliament, has said they 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.
His predecessor, Dr Rowan Williams, was strongly criticised for expressing his views about Government policy.
Meanwhile, the Prime Minister had a Mother's Day card delivered to his door by campaigners for new mums whose benefits are about to be capped.
Labour has accused the Government of imposing a mummy tax and said the welfare reforms are part of a series of austerity measures which unfairly target mothers.
Shadow minister for women Yvette Cooper MP told Sky News: It's like David Cameron and George Osborne have a blindspot about women because they're paying three times more than men in tax and benefit and pay and pension changes.
That is so unfair when women earn less and own less than men.
It shows that the Prime Minister and the Chancellor just don't get it and it's outrageous that new mums are hurt hardest.
Around 340,000 women claim either statutory maternity pay or maternity allowance every year.
Until now their benefits have gone up in line with inflation, which currently stands at 2.7%, according to the Consumer Price Index.
But from next month new mothers' benefits will go up by just 1% every year as part of a three-year cap on welfare increases.
So by 2015 critics have calculated the benefits will be effectively cut by ã180 because they will not increase by as much as the cost of living will.
