Group theoretical techniques are used to discuss the disordered hexagonal columnar-disordered rectangular columnar (D hd −D rd ) liquid crystal phase transition in HAT series. On the basis of Landau theory the transition is predicted to be second order. The Ginzburg-Landau-Wilson Hamiltonian corresponds to a universality class with an n=3 component order parameter and with cubic anisotropy. The critical behaviour near the D hd −D rd transition is discussed by referring to the renormalization group results of Aharony and other authors and we present evidence in favour of the critical value of n, n c , being greater than 3. It is also predicted that a second order transition from the D hd phase to an as yet experimentally undiscovered phase is possible Analyse de la transition en appliquant les techniques de la theorie des groupes