Is the Universe transparent to TeV photons?

If Lorentz invariance is broken at an energy scale Eq, as has recently been suggested in the context of attempts to quantize gravity, the kinematics of photon-photon collisions would be profoundly affected at lower energies. Specifically, electron-positron pair creation on soft photons may be forbidden at photon energies as low as 30 TeV times square root of (Eq/10**17 GeV) and the Universe would then be transparent to high energy photons. The proposition that Lorentz invariance is broken may be falsified by the techniques of TeV astronomy.