We have studied the lateral stability of planar reaction-diffusion fronts in an autocatalytic reaction between aqueous ions in an externally imposed electric field. In our experiments, migration drives the pattern formation leading to cellular structures where the sufficiently greater migrational flux of the reactant with respect to that of the autocatalyst is the driving force. The difference in electric field strength between the two sides of the thin reaction front results from the significant increase in conductivity during the reaction. The results of the theoretical analysis based on the empirical rate-law model of the reaction reproduce the behavior observed experimentally.