Hydromagnetic planetary-gravity waves propagating in a basic state zonal flow and zonal magnetic field both of which are sheared in the vertical direction are studied. It is found that the waves possess four critical levels at each of which they exhibit the valve effect behaviour, an effect due to the variation of density with latitude. It is also shown that on crossing a critical level the waves are either attenuated or escalated by an exponential factor which depends on the shear in the flow and the latitudinal variation in density.