I consider the superfield derivation of the effective theory of softly broken supersymmetry below the GUT scale. I point out the role of supergauge invariance in determining the form of the result, which is rather restricted in interesting classes of models. As an example I discuss sfermion mass splittings for matter embedded in a single GUT multiplet. Interesting differences arise between the cases of SU(5), SO(10) and E(6).