  We show that the piezoelectric coupling to three-dimensional phonons in GaAs
renormalizes the current-voltage exponent for tunneling of electrons into an
incompressible quantum Hall edge. The leading correction is always negative, in
agreement with experiments on the $\nu = 1/3$ state and, depending on the
precise value of the edge plasmon speed, can be as large as a few percent. We
also discuss higher-order corrections, which determine the effect of the
piezoelectric coupling in the extreme infrared limit.
