Theoretical study was performed earlier for the cell model of a charged porous membrane based on Onsager’s approach and the result was calculation of all electrokinetic coefficients. Experimental dependences of electroosmotic permeability, conductivity, and diffusion permeability of some perfluorinated membranes on electrolyte concentration were simultaneously and quantitatively described using exact analytical formulae based on the same set of physicochemical and geometrical parameters. It is shown here that for the developed cell model of the ion–exchange membrane, the Onsager principle of reciprocity is violated—the coupled cross kinetic coefficients are not equal. The violation is associated with the fact that the reciprocity principle takes place only for systems for which generalized fluxes are zero at thermodynamic forces other than zero within the framework of linear thermodynamics of irreversible processes.