The article discusses the current threat of international terrorism represented by so-called foreign terrorist fighters, that is persons, who leave the countries, where they live, to go to areas in the world, where there are conflicts, with the intention of supporting or promoting terrorist criminal acts or terrorist groups in various ways, or to dispense terrorist ideology. The author analyses the amendement of the Czech penal code carried out by act no. 455/2016 Sb., wich reacts to this threat by criminalising some actions, wich were not punishable before.