  In the presence of anisotropic cosmic expansions at global or local scale the
equations of electrodynamics in expanding space-time are modified and presented
here. A new effect should arise in regions of local anisotropic expansion in a
cosmologically isotropic background. These regions should naturally exist,
being connected with scales decoupling from the Hubble flow. Possible
observational consequences of this effect are suggested. In particular, I
predict the appearance or variation of the polarization of electromagnetic
radiation coming from or passing through these regions. This effect is
observable and possibly already observed in the polarization of quasars.
