Labour has attacked what it calls the "unbelievable hypocrisy" of Nick Clegg after the Liberal Democrat leader withdrew his party's support for the controversial bedroom tax policy.
The bedroom tax, officially called the spare room subsidy by the Department for Work and Pensions (DWP), was introduced in April 2013. It is a cut in housing benefit for recipients who have spare bedrooms.
But the policy has been accused by critics of being cruel. Many housing benefit recipients are unable to downsize because of a shortage in small properties, meaning they are trapped and fall into rent arrears as they struggle to make up for what was lost in the welfare payment reduction.
"This is unbelievable hypocrisy from Nick Clegg," said Rachel Reeves, Labour's shadow work and pensions secretary.
"The Lib Dems voted for the bedroom tax. There wouldn't be a bedroom tax if it wasn't for the Lib Dems. And in February when Labour tabled a bill to scrap the bedroom tax, the Lib Dems were nowhere to be seen.
"This just goes to show why you can't trust a word the Lib Dems say - it is clear the only way to cancel the bedroom tax is to elect a Labour government next year."
The government argues it is unfair for taxpayers to fund the spare rooms of those on benefits. And it wants to free up larger properties for those who need more rooms.
However, official figures show that just 6% of those affected have been able to downsize.
Danny Alexander, chief secretary to the Treasury, wrote in The Mirror that he and Clegg reviewed their support of the policy and decided that it needs reform, such as an exemption for the disabled and those who cannot find smaller homes to move to.
"Overwhelmingly, our benefit reforms are working, resulting in many more people gaining the independence and self respect of re-entering work," Alexander wrote.
"However with only one in 20 of affected claimants having successfully downsized, it's clearly time to take stock and change our approach in this particular area."
Two-thirds of housing association tenants hit by the bedroom tax have been pushed into rent arrears as a result of Britain's most controversial welfare policy.
According to a poll of 183 housing associations by the National Housing Federation (NHF), an organisation which represents their interests, 66% of their residents affected by the bedroom tax are in rent arrears. Over a third, 38%, are also now in debt as a result.