We consider binary-encounter electron emission in relativistic ion-atom collisions in the presence of a monochromatic low-frequency plane-wave electromagnetic field of circular polarization. The parameters of the field---its intensity and frequency---are chosen in such a way that the field per se has a negligible effect on the initial (ground) state of the atom. The results show, however, that this field may have a profound effect on the electron emission spectra, which is mainly caused by an enormous energy exchange between the emitted electron and the field.