  A recent paper by Gambini, Rastgoo and Pullin [arXiv:1106.1417 investigates
the important issue of constraints from Lorentz invariance on Planck scale
physics, arguing that the classic analysis of Collins, Perez, Sudarsky, Urrutia
and Vucetich \cite{cpsuv} is not generally valid. We argue that the new work is
based on models that do not capture the relevant physics, and that almost all
models of observable high energy Lorentz violation, and proposed
Lorentz-violating theories of quantum gravity, are ruled out by low energy
tests; the only known exceptions are based on supersymmetry.
