Using group theory we classify the nonlinear magneto-optical response at low-index surfaces of fee antiferromagnets, such as NiO. Structures consisting of one atomic layer are discussed in detail. We find that optical second-harmonic generation is sensitive to surface antiferromagnetism in many cases. We discuss the influence of a second type of magnetic atoms, and also of a possible oxygen sublattice distortion on the output signal. Finally, our symmetry analysis yields the possibility of antiferromagnetic surface domain imaging even in the presence of magnetic unit-cell doubling.