  We study the twist-3 three-gluon contribution to the single spin asymmetry in
the light-hadron production in pp collision in the framework of the collinear
factorization. We derive the corresponding cross section formula in the leading
order with respect to the QCD coupling constant. We also present a numerical
calculation of the asymmetry at the RHIC energy, using a model for the
three-gluon correlation functions suggested by the asymmetry observed in the
$D$-meson production at RHIC.
