We consider an arbitrary supersymmetric U(1) gauge factor at the TeV scale, under which the two Higgs superfields H_1,2 of the standard model are nontrivial. We assume that there is a singlet superfield S such that H_1 H_2 S is an allowed term in the superpotential. We discuss first the generic consequences of this hypothesis on the structure of the two-doublet Higgs sector at the electroweak energy scale, as well as Z-Z' mixing and the neutralino sector. We then assume the existence of a grand

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... unified symmetry and universal soft supersymmetry breaking terms at that scale. We further assume that the additional U(1) is broken radiatively via a superpotential term of the form h h^c S, where h and h^c are exotic color-triplet fields which appear in E_6 models. We show that the U(1) breaking scale and the parameter tan(beta) ≡ v_2/v_1 are then both predicted as functions of the H_1 H_2 S coupling.