We present measurements of the (e, 2e) cross sections of xenon for transitions leading to the and states of the residual ion using an incident polarized electron beam in coplanar asymmetric kinematics and in the intermediate energy regime. The results show that the spin up - down asymmetry for the and transitions can be understood as an analogue of the so-called fine-structure effect in inelastic scattering. However, our present measurements also point to significant contributions from relativistic effects in the electron - atom system under certain conditions. The measured spin up - down asymmetry is analysed using the density matrix formalism. This approach reveals that different exchange interactions contribute to the fine-structure effect for ionization. The contribution of relativistic interactions in the observed parameters is also investigated by using a semirelativistic DWBA model to evaluate the scattering amplitudes.