Thousands of people will take part in a "mass sleep out" tonight to protest against the "bedroom tax" and other welfare changes.
People will gather in towns and cities across the UK, including London, Edinburgh, Belfast, Cardiff, Liverpool, Manchester and Leeds, and sleep on the streets to draw attention to the effects of the controversial measures.
One of the organisers, Rick Victory, 46, of Cheltenham, said: "We expect at least 3,000 people to take part in the 60-plus events.
"We fear that the cuts will push people who cannot afford to move into the private rented sector towards homelessness.
"Our aim is primarily to engage with the public, to change public opinion which can see the people involved as scroungers, and make them realise the people who are affected are often low paid workers and disabled people."
The Government's withdrawal of housing benefit from social tenants with spare rooms - officially described as a ''spare room subsidy'' - is described as a "bedroom tax" by critics.
The measure is in reality a cap on housing benefits introduced in April and aimed at tenants deemed to be living in social accommodation with extra bedrooms.
Under new ''size criteria'', tenants with one spare bedroom have had a payment reduction of 14% and those deemed to have two or more spare, a reduction of 25%.
Expected to save about £500 million annually, the measure is part of the Government's deficit reduction strategy and bid to tackle ''welfare dependency and unaffordable spending''.
The Government says a system of additional funding in the form of discretionary housing payments (DHPs) through local authorities is in place for those in difficulties, including the disabled, but opponents say the funds are insufficient.
A Department for Work and Pensions spokesman said: "It is simply not affordable to pay housing benefit for people to have spare rooms. Reforms to housing benefit in the social sector mean families receive help for the number of bedrooms they need, and these are exactly same rules as in the private sector.
"However, we are giving local authorities £190m funding this year so vulnerable claimants get the help they need during the welfare reforms."
Protesters braved the rain in Brixton, south London, to set up tents and gazebos for their overnight stay in Windrush Square.
Organiser Gr ace Lally, 34, said she believed the poorest in society were being targeted by the so-called bedroom tax after 170 people on Brixton's Loughborough estate where she lives were affected.
"I know the hardship this is causing is totally unnecessary," she said.
"I think it's vindictive to go after the poorest people in our society and to blame them for the lack of housing.
"I feel it's really important we stand up for those people.
"You're only penalised for having a so-called spare bedroom if you're unemployed and you're poor.
"People are very passionate about this issue and this is not going to be the last protest we have."
In Glasgow, protesters set up a camp in front of the Kelvingrove Art Gallery and Museum, opposite the office of MSP Ruth Davidson, leader of the Scottish Conservatives.
Gail Morrow from the Scottish Anti Bedroom Tax Federation said: " The support on the day has been fantastic in Glasgow, with local businesses keeping us refreshed with lunch. The passing support has been amazing, with people stopping to talk and show support.
"The response from the campaigns has been tremendous in such a short space of time. The speed of the mobilisation shows the strength of our anti-eviction army."
John Park from the North Lanarkshire campaign group said: "The showing of solidarity today has been overwhelming. It is important that we step up to the task of defending our vulnerable neighbours."