Analiza i ocena regulacji uszczelniających system opodatkowania dochodów przedsiębiorców w Polsce w latach 2015–2019

The article looks at the legal solutions adopted in 2015–2019 in Poland in order to tighten the tax system. In the field of income taxes, these were anti-abusive regulations, securing the tax system in a general way, as well as targeting specific tax avoidance schemes. The first part of the article discusses the factors deter­mining fiscal efficiency which is the main criterion adopted in the study. In the next part the most important tax solutions sealing the system are presented. In the third part an attempt was made, using a number of indicators, to answer the question whether the observed increase in tax revenues from corporate income taxes can be attributed to the anti-abusive measures which were taken. Based on the conducted research, it has been shown that the decreasing tax gap is the result of the improvement in tax collection effectiveness in connection with the adopted sealing measures.