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.
Campaigners gathering on Saturday in more than 50 towns across the UK say the move targets the most vulnerable in society.
It is expected to affect 660,000 people when it comes into effect next month.
The protest's national organiser, Dr Eoin 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."
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.