Abstract
Purpose: The issue of taxation of the financial sector has long been widely discussed both in the European Union and in other countries of the world. It is extremely important to construct a proper tax, which would ensure the objectives set for it, and at the same time would generate as little negative effects as possible and would be as little burdensome for taxpayers as possible. The aim of the study is to verify the hypothesis that banks in Poland use the possibility of purchasing treasury bonds in order to lower the tax base. Methods: The paper analyses the use of treasury securities as an instrument of tax optimisation. The study includes theoretical and empirical research. A descriptive comparative analysis has been used to assess if after the introduction of the tax on some financial institutions there was an increase in treasury bond purchases in the last days of the month and an increase in sales at the beginning of the following month. Results and conclusions: The author confirmed the research hypothesis that banks in Poland use the possibility of buying treasury bonds in order to lower the tax base.