He-broadening coefficients are measured for 28 lines of ¹²CH₃F in the ^RQ_O (K_i = 0, ΔK = 1, ΔJ = 0) and ^RQ₆ (K_i = 6, ΔK = 1, ΔJ = 0) branches of the v₆ band, using a tunable diode laser spectrometer. The collisional widths obtained by fitting Rautian profiles to the measured shapes of the lines are slightly larger than those derived from Voigt profiles. The broadening coefficients for the lines belonging to the same low J transitions are significantly greater in the ^RQ₀ branch than in the ^RQ₆ branch. Moreover, they decrease on the whole with increasing J in the ^RQ₀ branch and tend to increase from J varying from 7 to 10 in the ^RQ₆ branch. These trends may be approximately reproduced by calculations based on a semiclassical impact theory of collisional broadening.