Protests have been staged in a series of cities against government plans to cut housing benefit for those considered to have too much space.
Protests against the plan - labelled the "bedroom tax" by Labour - have been held in at least 10 towns and cities, including Manchester, Birmingham and London.
The welfare changes, due in April, are expected to affect 660,000 people.
No 10 says the policy will address pressure on social housing.
Those deemed to have a spare room in their council or housing association home will have their housing benefit claims reduced.
The protests' national organiser Eoin Clarke - founder of the think tank Labour Left - said: "This is a cruel policy that primarily hits single parents, and the adult disabled.
"Even children deemed disabled but not 'severely' so, are affected. Carers, the terminally-ill, battered wives and husbands are all affected.
"Soldiers living in single accommodation or indeed foster parents with more than one foster child are hit, despite the government's talk of a U-turn.
"There are times in history when people must stand together in defence of common decency - that time has come."
Protesters turned out for Saturday's demonstrations in cities including Birmingham, Hull, Manchester, Durham, Exeter, Leicester, Brighton, Sheffield, Derby and Nottingham.
'Spare room subsidies'
The government estimates that roughly a third of social sector claimants will have their benefit cut. Only those of working age will see reduced payments.
But foster carers and families of armed services personnel will be exempt from controversial changes to housing benefit, ministers have said.
Prime Minister David Cameron and Labour leader Ed Miliband have been involved in a fierce war of words over the issue for weeks, with the Mr Miliband branding the policy as a "bedroom tax".
The prime minister has insisted the proposals are not a tax and will, instead, see curbs on what he has called existing "spare room subsidies".
No 10 has defended the policy as a whole, saying it was important to address pressure on social housing waiting lists and growing overcrowding.