The article attempts to give a comprehensive analysis of the legal and parliamentary practice in Poland, made after four years from the adoption of the Treaty of Lisbon. The special focus is given to three issues: regulations of the so-called cooperation law, regulations of the Rules of Procedure of the Sejm for the Committee of the European Union and the practical aspects of proceedings of the EU legislative proposals in the Sejm. The starting point of the above analysis is protocol on the application of the principles of subsidiarity and proportionality, introduced by the Treaty of Lisbon, which impose on the EU institutions to directly inform national parliaments of the content of EU legislative proposals for which is provided to express an opinion. Therefore, the Lisbon’s Treaty confers on Polish parliament the power having the nature of a veto in relation to decision reducing sovereign rights of Poland as the one of the member states. However, the present role of the Sejm in the functioning of the EU depends on its ability to exert a real influence on the European policy conducting by the government, which is related with a possibility of concluding the political consensus on the national level. The author suggests that for supervision of the EU’s principles of subsidiarity and proportionality, not only greater activeness of Polish parliament, but also providing mechanisms for the enforcement of the members of the Council of Ministers of the political responsibility for their actions in the EU institutions, is required. Otherwise, the solutions adopted in the Treaty of Lisbon will not affect on the existing European policy way in Poland, which leads government.