The effect of uniaxial stress on terahertz stimulated emission from phosphor and antimony donors in silicon excited by CO2 laser radiation was studied. The laser action originates from 2p0→1s(T2) intracenter transitions. A compressive force applied to the silicon crystal decreases the laser threshold by one order of magnitude. The output power depends nonmonotonically on the stress, while the emission frequency does not change. The results are explained by changes of the donor electronic structure, which do not affect the energy gap between the laser states, and a resonant interaction with acoustic f-TA and g-TA phonons that disappears with increasing stress.