This paper discusses the features of methods used to synthesize a discrete-event supervisor for a group control system of mobile robots. We consider the upper levels of a group control system as a discrete-event system. Su-pervisor synthesis methods for such a system and the evaluation of their computational complexity are presented. The paper highlights the limitations of the best method in terms of computational complexity and proposes a modi-fication that allows to remove these limitations without increasing the computational complexity. The application of the modified method is demonstrated on the example of synthesizing a supervisor for the group action of a fire-fighting operation by three robots.