In a strained layer grown epitaxially on a substrate, the motion of a dislocation on any particular glide plane in the layer can be influenced by the presence of dislocations on other glide planes. The focus here is on the glide of a dislocation extending from the free surface of the layer to the layer‐substrate interface, the so‐called threading dislocation. A general definition of driving force for glide of a threading dislocation in a nonuniform stress field is adopted to calculate the driving force on a threading dislocation due to an encounter with an interface misfit dislocation on an intersecting glide plane. The result is examined in detail for the case of cubic materials, taking into account different combinations of Burgers vectors. The analysis makes it clear that the misfit dislocation forces the threading dislocation to glide through a channel of width less than the full layer thickness. A blocking criterion is proposed, based on the presumption that blocking will occur if the channel width is less than the critical thickness for the local reduced strain. The results indicate that this effect can be significant in blocking the glide of a threading dislocation, depending on the mismatch strain magnitude and the layer thickness.