Bedroom Tax Protest March, Glasgow, 2013

The under-occupancy penalty (also known as the under occupation penalty, under-occupancy charge, under-occupation charge or size criteria) results from a reform contained in the British Welfare Reform Act 2012 whereby tenants living in public housing (also called council or social housing) with rooms deemed "spare" face a reduction in Housing Benefit, resulting in them being obliged to fund this reduction from their incomes or to face rent arrears and potential eviction by their landlord (be that the local authority or a housing association). The under-occupancy penalty is more commonly referred to as the Bedroom Tax; especially by critics of the changes who argue that they amount to a tax because of the lack of social housing (or in some areas, any rented accommodation) for affected tenants to downsize to (and the refusal to accept the risk of taking in lodgers). Quoted from Wikipedia