  We show that the transverse polarization asymmetry of the $\tau$-lepton in
the decay $t\rightarrow b \tau \nu$ is extremely sensitive to CP violating
phases arising from the charged Higgs exchange in the Weinberg model of CP
non-conservation. Qualitatively, the polarization asymmetries are enhanced over
rate or energy asymmetries by a factor of $\approx {m_t\over m_\tau}\approx
O(100)$. Thus for optimal values of the parameters the method requires $\approx
10^4$ top pairs to be observable rather than $10^7$ needed for rate or energy
asymmetries. We also examine $\tau$ polarization in b decays via $b \rightarrow
c \nu \tau$ and find that it can also be very effective in constraining the CP
violation parameters of the extended Higgs sector.
