In this paper the author deals with transnational effects of decisions of the Antimonopoly Office of the Slovak Republic as an authority for the protection of competition of the national nature, however, in the European law context. The author points out the application of national competition law in close association with legal provisions contained in the essential documents of the EU. The paper also mentions the European tendencies of unifying competition protection legislation. In the context of a threat to competition, the author also points out the importance of complying with obligations in detecting and proving the same. He also refers to situations where, despite the potential presence of competition concerns, competition distortions do not occur.