Protests are taking place nationwide against a new "bedroom tax" that will cut benefits to people with a spare room.
Under the government's welfare reforms, those deemed to have a spare bedroom in their council or housing association home will have their housing benefit claims reduced by £40 to £80.
Labour has dubbed the move the "bedroom tax". However David Cameron prefers the term "spare room subsidy", arguing it is a change in benefit payments not the imposition of a new tax.
Campaigners gathering in more than 50 towns say the move targets the most vulnerable in society.
It is expected to affect 660,000 people when it comes into effect next month. A number of MPs are joining the march with dozens of local councillors and campaigners, who have been tweeting their support.
One Labour MP has been calling on councillors not to evict any victim of bedroom tax who falls behind on rent.
The protest's national organiser, Dr Èoin Clarke, 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."
Iain Duncan Smith confirmed that foster carers and members of the Armed Forces will not be subjected to the government's controversial so-called "bedroom tax" earlier this week. However campaigners say the U-turn has not gone far enough.
Asked by ITV News whether his policy was unravelling, Duncan Smith replied there were "no climb-downs at all".
"This policy is absolutely vital. The last government saw many people living in accommodation they did not fully occupy," he said.
According to the National Housing Federation (NHF) those affected also include separated parents who share care of their children and couples who use a spare bedroom when recovering from an illness or operation.
Gregor Cubie a journalism student from Glasgow, wrote in blog for the Huffington Post UK that "the hurt, frustration and anger provoked by 'bedroom tax' is causing rumblings in Glasgow's underbelly which could unleash the kind of wave of civil unrest that has defined the city's politics over the last century."
He goes on to explain why bedroom tax provokes such anger saying Glasgow is "a city in which a reported 90,000 people receive housing benefit, many of whom live in houses with unoccupied bedrooms. The lack of single-bed social housing means that few will be able to downsize and avoid the 14%-25% penalty for 'under-occupancy'. The added fact that 60-70% of those penalised are disabled has stoked the outrage of the working class and the political left to the point of combustion."Suggest a correction