We have investigated the high-order above-threshold ionization (HATI) spectrum of formic acid by means of high-resolution electron spectroscopy using 800-nm femtosecond laser light.The resonance-like enhancement structures in the HATI spectrum are shown to be experimentally reproducible and three enhancement-suppression patterns are observed in different energy regimes with increasing laser intensity.The agreement between experiment and theory shows that "channel closing" effects play an important role in the observed resonance-like enhancements (RLEs).The existence of the RLEs for formic acid, which lacks any symmetry, shows that molecular symmetry does not affect the RLEs.