In dubio pro tributario, as an unwritten rule of tax law, has existed for many years. On the 1st January 2016 the rule was explicitly included in The Tax Ordinance Act. Tax authorities treat the newly introduced in Artilce 2a The Tax Ordinance Act rule with caution. In dubio pro tributario is most often used by administrative courts when, after applying all the stages of interpretation, the provision remains questionable.