Electromagnetic effects on the critical ionization velocity (CIV) process become important when the neutral gas velocity Vn exceeds the local Alfv¿n speed VA. The electron heating due to unstable lower hybrid waves necessary for CIV still occurs, but the efficiency of the electron heating is significantly reduced when the electromagnetic effect comes into play. This is verified by a series of simulation runs using two-dimensional electromagnetic particle code combined with PANIC. The significance of the electromagnetic effects for the occurrence of CIV in the comet--solar wind interaction and other space phenomena is briefly discussed. We find that the comet environment is marginal for the excitation of CIV.