[en] The infrared and Raman spectra were measured on the edge plane of the single crystals of quasi-two-dimensional organic conductors α-(BEDT-TTF)₂MHg(SCN)₄(M=NH₄ and K) to look for experimental evidence for the charge-ordering fluctuation. In the optical conductivity spectra for K-salt, four charge sensitive ν₂₇ modes, three of which are infrared active when inversion symmetry exists, were found at around 200 K. From the simple symmetry consideration, the finding of four ν₂₇ modes gives evidence for the breaking of inversion symmetry, which is probably associated to charge-ordering fluctuation. In contrast, NH₄-salt was found to keep the inversion symmetry down to 7.3 K.