George Osborne is going to fight back over benefit cuts, accusing church leader critics of "depressingly predictable outrage."
The Chancellor will turn his fire on "vested interests" that have been attacking the controversial reforms, including the so-called 'bedroom tax' and cuts to council tax benefits.
And he will tell charities, churches and opposition politicians they are on the "wrong side" of public opinion.
It comes after a petition calling for Work and Pensions Secretary Iain Duncan Smith to prove he could live on £53 a week passed 115,000 signatures.
On Sunday, a coalition of church leaders said the measures would target the poorest.
But speaking at a supermarket in Kent on Tuesday, Osborne will say: "Those who defend the current benefit system are going to complain loudly.
"These vested interests always complain, with depressingly predictable outrage."
Defending "every line" of welfare spending is not "credible," he will say, insisting that nine out of 10 working households will be better off as a result of the welfare and tax changes.
"Because defending benefits that trap people in poverty and penalise work is defending the indefensible," Osborne will say.
"The benefit system is broken; it penalises those who try to do the right thing; and the British people badly want it fixed.
"We agree - and those who don't are on the wrong side of the British public."
Meanwhile, research from the Resolution Foundation said those on lower and middle incomes would see any gain from tax cuts swallowed up by reductions in benefits.
As the new Universal Credit is based on post-tax income, around two-thirds of the effect of a rise in the tax-free allowance would be offset by a reduction in their benefits.
By contrast, better-off families who do not get Universal Credit would pocket the full amount.
The think-tank's associate fellow, Donald Hirsch, said: "If the Government really wants to help low earning families through tax cuts, it will need to adjust Universal Credit so that they receive at least the same benefit as those higher up the income scale.