In turn, shifting taxes to immovable property could pose serious transitional challenges as vertical and horizontal inequities could arise, as well as spikes in tax liabilities for some households. For instance, in Sweden, Sorensen (2010) reports that reforms in 2008 increased the bias in favour of investing in housing relative to other assets largely due to strong political opposition to property taxation. As noted, with property taxation in many countries a principal source of sub-national government revenue, shifting the tax mix toward immovable property taxation can often encounter resistance at the sub-national level. Where sub-national governments receive transfers from the national treasury, increasing taxation of immovable property can be unattractive if such an effort results in reduced budgetary transfers or revenue sharing from the centre (e.g. Czech Republic, Hungary, Poland).