  We present the threshold resummation for the single spin asymmetry in heavy
flavor production by linearly polarized photons. We analyze the soft-gluon
contributions to the asymmetry at fixed order in $\alpha_s$ to the
next-to-leading logarithmic accuracy. Our analysis shows that, contrary to the
production cross section, the azimuthal asymmetry is practically insensitive to
soft radiation. Our calculations of the asymmetry up to the 6th order in
$\alpha_s$ lead only to small corrections (of order of few percent) to the Born
predictions at energies of the fixed target experiments. Fast convergence of
the perturbative series for the azimuthal asymmetry is due to the factorization
properties of the photon-hadron cross section. We conclude that measurements of
the single spin asymmetry would provide an excellent test of pQCD applicability
to heavy flavor production.
