  The Chern-Simons-type term in the photon sector of the Lorentz- and
CPT-breaking minimal Standard-Model Extension (mSME) is considered. It is
argued that under certain circumstances this term can be removed from the mSME.
In particular, it is demonstrated that for lightlike Lorentz violation a field
redefinition exists that maps the on-shell free Chern-Simons model to
conventional on-shell free electrodynamics. A compact explicit expression for
an operator implementing such a mapping is constructed. This expression
establishes that the field redefinition is non-local.
