We reveal for the first time through a theoretical first-principles study that the adsorption of a nonmagnetic π-conjugated organic molecule on a ferromagnetic surface locally increases the strength of the magnetic exchange interaction between the magnetic atoms binding directly to the molecule. This magnetic hardening effect leads to the creation of a local molecular mediated magnetic unit with a stable magnetization direction and an enhanced barrier for the magnetization switching as compared to the clean surface. Remarkably, such a hybrid organic-ferromagnetic system exhibits also a spin-filter functionality with sharp spin-split molecularlike electronic features at the molecular site.