  We consider the contributions of the extra gauge boson Z' to the like sign
$\tau$ production process $e^-\gamma\to e^+(\mu^+)\tau^-\tau^-$, induced by the
tree-level flavor changing interactions. Since these rare production are far
below the observable level in the Standard Model and other popular new physics
models such as the minimal supersymmetric model, we find that Z' can give
significant contributions to this process, and with reasonable values of the
parameters in TC2 models, the cross section can reach several tens of fb and
may be detected at the $e\gamma$ collisions.

High Energy Physics - Phenomenology