  We consider theories where lepton flavor is violated, in particular
concentrating on the four fermion operator consisting of three electrons and a
tau. Strong constraints are available from existing searches for tau -> eee,
requiring the scale of the contact interaction to be less than ~(9 TeV)^-2. We
reexamine this type of physics, assuming that the particles responsible are
heavy (with masses greater than ~TeV) such that a contact interaction
description continues to be applicable at the energies for a future e+e-
collider. We find that the process e+e- -> e tau can be a very sensitive probe
of this kind of physics (even for very conservative assumptions about the
detector performance), already improving upon the tau decay bounds to less than
~(11 TeV)^-2 at collider energy sqrt(s) 500 GeV, or reaching beyond ~(35
TeV)^-2 for sqrt(s) = 3 TeV. Even stronger bounds are possible at e-e-
colliders in the same energy range.
