With the development of the Union and its laws, its powers are gradually expanding. With that in mind, the question arises as to whether, and in what way, national parliaments can influence the adoption of regulations in the European. This paper deals with the scrutiny over the European Union legislation by national parliaments. The national parliaments oversight of EU legislation is conducted through the so-called subsidiarity control mechanism. This power is granted to the national parliaments under Article 12 of the Treaty on European Union and the Protocol (No 2) on the application of the principles of subsidiarity and proportionality. The principle od subsidiarity requires action by the Union in areas where the Union does not have exclusive competences, only when the proposed action can be better achieved at Union level, while the principle of proportionality requires that porposed measures do not go beyond what is sufficient to achieve Union objectives. Scrutiny of the principle of subsidiarty is not he only area in which national parliaments have an influence on Union policy. Relations between national parliaments and the Union are also maintained through political dialogue between national parliaments and the Commission. Through their involvement in decision-making within the European Union, national parliaments contribute to building a just and democratic Union.