A new mechanism for inducing bulk asymmetry and second order optical nonlinearity in polymer-dye systems is described. An anisotropic distribution of charges is established inside the medium resulting from the application of high voltage via an asymmetric electrode structure. The nonlinearity induced via this mechanism is perpendicular to the externally applied electric field. It is proven that the nonlinearity induced by charge injection cannot arise from dipolar alignment of molecules, but rather results from the nonlinearity of charged dye dimers in a bulk charge gradient.