Double Spin Asymmetries in Charmonium Hadroproduction at HERA-$\vec N$

We discuss the double spin asymmetries in charmonium hadroproduction with nonzero transverse momenta at fixed target energies, $\sqrt{s}\simeq40$ GeV, within the framework of the factorization approach. It is shown that the color octet contribution is dominant in the asymmetries. The size of the asymmetries and the projected statistical errors in a future option of HERA with longitudinally polarized protons scattering off a polarized target (HERA-$\vec N$) should allow to distinguish between different parametrizations for the polarized gluon distribution in the proton.