  We address the study of gauge invariance in the Standard Model Extension
which encompasses all Lorentz-violating terms originated by spontaneous
symmetry breaking at the Planck scale. In particular, we fully evaluate Ward
identities involving two and three point functions and derive the conditions
which assure gauge invariance of the electromagnetic sector of the Standard
Model Extension at one-loop. We show that momentum routing invariance is
sufficient to fix arbitrary and regularization dependent parameters intrinsic
to perturbation theory in the diagrams involved. A scheme which judiciously
collects finite but undetermined quantum corrections is employed, a
particularly subtle issue in the presence of $\gamma_5$ matrices.
