  A consistent quantization scheme for imaginary-mass field is proposed. It is
related to an appropriate choice of the synchronization procedure (definition
of time), which guarantee an absolute causality in agreement with Lorentz
covariance. In that formulation a possible existence of field excitations
(tachyons) distinguish an inertial frame (tachyon privileged frame of
reference) {\em via} spontaneous breaking of the so called synchronization
group. In this scheme relativity principle is broken but Lorentz symmetry is
exactly preserved in agreement with local properties of the observed world.
