The pressure tensor profile, in the vicinity of the planar interface between isotropic liquid and nematic liquid crystal phases of rod-like molecules, is calculated using Onsager's density functional theory. Two different conventions for the transverse pressure, due respectively to Harasima and to Irving and Kirkwood, are shown to give distinguishable, but similar, forms. The equivalence of these definitions with those based on the grand potential density is clarified. The profiles, and the location of the surface of tension, depend dramatically on the orientation of the director relative to the interface. These physical differences are much larger than the ambiguities associated with the different pressure conventions.