Abstract-In the method of moments (MoM) electric field integral equation (EFIE) analysis of slabs of metamaterials, we show that a left-preconditioning scheme by blocks gathering interactions between basis functions belonging to each basic cell of the metamaterial reaches convergence in less iterations and with less computational time than a left-preconditioner based on discarding interactions between basis functions beyond a given distance.Index Terms-Electromagnetic scattering, method of moments (MoM), numerical analysis, preconditioning.