We have studied a model of the order-disorder phase transitions in CsLiSO₄ and CsLiCrO₄. In this model a BX₄ tetrahedron has four equilibrium orientations in a disordered hexagonal phase. The constants of the interaction between ordered BX₄ groups are calculated in the framework of the electrostatic model. It is shown that these constants have a competitive nature. The Monte Carlo method is applied to study the phase diagrams and thermodynamic properties of the phase transitions. The results obtained are in good agreement with experimental data.