The total burden of taxes on labor across 34 OECD countries rose to 35.9 percent in 2013 from 35.7 percent in 2012, according to a new OECD report released on Friday. In its annual Taxing Wages 2014 publication, the Paris-based Organization for Economic Co-operation and Development (OECD) said personal income tax has risen in 25 out of 34 OECD countries over the past three years, as countries reduce the value of tax-free allowances and tax credits and subject higher proportions of earnings to tax. It said the increases in tax burdens on labor income in 2013 were largest in Portugal, the Slovak Republic and the United States. The report said the tax burden increased in 21 out of 34 countries, fell in 12, and remained unchanged in one. The 2013 rise follows a substantial increase in 2011 and a smaller one in 2012. Since 2010, the tax burden has increased in 21 OECD countries and fallen in 9, partially reversing the reductions seen between 2007 and 2010. The tax and social security contribution burden is measured by the tax wedge as a percentage of total labor costs, or the total taxes paid by employees and employers, minus family benefits received, divided by the total labor costs of the employer. Taxing wages also breaks down the tax burden between personal income taxes, including tax credits, and employee and employer social security contributions.