Measurements are reported for kinematically complete electron-impact ionization collisions with oriented 3P sodium atoms excited from the ground state by right- and left-hand circularly polarized light. The mea-surements reveal a strong dependence of the ionization cross section on the helicity inversion of the exciting photon. This dichroic effect and the magnetic state resolved cross sections are described using the distorted-wave Born approximation and the dynamically screened Coulomb wave method. Within the context of these methods we investigate the role of different short- and long-range interactions involved in the process. For moderate values of incident energy we conclude that the shape and magnitude of the dichroism is predomi-nantly determined by the Coulomb interactions of the outgoing electrons with the residual ion. For slow escaping electrons the dichroism is also influenced by the interelectronic correlations.