Cutting benefits for social tenants with spare rooms is "common sense", Tory chairman Grant Shapps has said as he hit back at protests against a major welfare squeeze.
Churches, charities and campaign groups joined Labour in an assault on the biggest shake-up of the system of state help for 60 years which starts to take effect on Monday.
But Mr Shapps insisted wide-ranging reforms were vital to tackle the deficit, would encourage people off benefits and into work, and help ease housing shortages.
The under-occupancy penalty, dubbed a "bedroom tax" by opponents and a "spare-room subsidy" by ministers, has become the focus for protests.
From Monday, around 660,000 families will lose an average £14 housing benefit a week in a move ministers hope will save £500 million a year.
Charities say it will lead to homelessness and rising demand for food banks and will hit the disabled hardest - with children among a group challenging the policy in court. It sparked an attack by a coalition of churches who said vulnerable people were paying a "disproportionate price" under the Government's austerity drive.
Mr Shapps rejected the criticisms and defended the housing benefit cut. "Where were these people jumping up and down as those housing waiting lists doubled under the previous administration?" he asked on BBC Radio 4's The World This Weekend.
"Why weren't we hearing from the churches, why weren't we hearing from these Labour politicians? We have a million spare bedrooms which are not being used and yet we are paying housing benefit to support.
"Wouldn't it be better to put some of those people who are languishing on those record housing waiting lists into homes by freeing up those spare bedrooms?"
He told Sky News: "It is wrong to leave people out in the cold with effectively no roof over their heads because the taxpayer is paying for rooms which aren't in use. It's just a common-sense reform which in the end will help house more people."