Clarification over how many people in Scotland may have been wrongly hit by the so-called bedroom tax has been demanded by the Scottish Government.
Scotland's Welfare Minister Margaret Burgess said she will press for answers when she meets Lord Freud, the UK Government's Minister for Welfare Reform, in London later today.
Earlier this month, it emerged that thousands of social housing tenants in the UK are in line for money back after being wrongly hit by the "bedroom tax".
A loophole in the Westminster Government's welfare reforms means that what UK ministers call the spare-room subsidy does not apply to certain renters who have lived in the same home for more than 17 years.
Housing experts reportedly said that 40,000 UK claimants could be affected, but the Department of Work and Pensions (DWP) stressed that it believes a maximum of 5,000 tenants are likely to have been caught up.
Speaking ahead of the meeting with Lord Freud, Mrs Burgess said: "I am deeply disturbed to hear reports that some of Scotland's most vulnerable people could have been overcharged.
"Lord Freud needs to provide answers so we can understand how many people may have been affected by this Department of Work and Pensions error.
"Westminster now needs to take action. We need to know what steps are being taken to compensate those people who have wrongfully had their housing benefit withdrawn."
She added that the Westminster Government has "a lot to answer for", with people "struggling to pay their bills because of the bedroom tax".
"There was no justification for introducing the bedroom tax to reduce housing benefit expenditure in the Scottish social rented sector, especially when we see the financial and social costs affecting society's most vulnerable," she said.
"We know that 80% of households affected by the bedroom tax contain an adult with a recognised disability, and over 12,000 children are affected. That's why we have consistently expressed our opposition to this measure."
Scottish Ministers have committed £20 million in the 2014-15 Budget Bill to supporting those affected by the so-called bedroom tax.
The DWP rejects the "bedroom tax" tag and says the reality is that "a spare room subsidy" has been removed from social sector tenants.
A DWP spokeswoman said: "The removal of the spare room subsidy is necessary to return fairness to housing benefit and we have given councils in Scotland over £13 million in 2013/14 to support vulnerable people who need extra help through our reform.
"Even after the policy change we still pay the majority of most claimants' rent, but it's simply not affordable to pay housing benefit for people to have spare rooms."
Meanwhile, Holyrood's Welfare Reform Committee is to consider a petition on the issue.
The petition, lodged in October last year on behalf of the No2BedroomTax Campaign, calls on the Scottish Parliament to urge the Scottish Government to make around £50 million available "to mitigate all effects of the bedroom tax in Scotland".