The UK Government says "the taxpayer can no longer afford to cover the costs of spare bedrooms" for social housing tenants, but it has made extra money available to support vulnerable people affected by the spare room subsidy, commonly known as the bedroom tax.
The way the system works is that tenants classed as having one spare bedroom lose 14 per cent of their housing benefit, while those with two or more spare bedrooms lose 25 per cent.
It is targeted at reducing under-occupancy of social housing.
There are 90,000 households on council waiting lists in Wales.
The UK Government points out that claimants can decide whether to pay the difference, or move to smaller accommodation - and councils have discretion over whether disabled children should be allocated their own bedrooms.
– Department for Work and Pensions spokesperson
Housing benefit continues to pay the vast majority of people's rent, but the taxpayer can no longer afford to cover the costs of spare bedrooms.
However, we have made £6.2m available to Welsh councils to support vulnerable people, with an additional £880,000 available to help those in rural parts of Wales.