The ferromagnetic square lattice Ising spin system is dynamically coupled to another set of Potts variables τ. We show that the usual Ising phase transition is universally preserved, but the transition temperatureTc is shifted upwards. To investigate the transition and to calculateTMc we use both a method by Muller-Hartmann-Zittartz as well as a systematic expansion about the soluble Ising limit. The comparison shows that the MHZ-formula forTc is presumably a very accurate fit to the correct transition temperature. The results are relevant for special cases of more generalq-state models, for instance the Ashkin-Teller model.