Using group theory techniques, we investigate the mathematical relationship between baryon number, lepton number, and operator dimension in the Standard Model effective field theory (SMEFT), when flavor symmetries are present. For a large set of flavor symmetries, the lowest-dimensional baryon- or lepton-number violating operators in the SMEFT with flavor symmetry are of mass dimension 9. As a consequence, baryon- and lepton-number violating processes are further suppressed with the introduction of flavor symmetries, e.g., the allowed scale associated with proton decay is typically lowered to 10(5) GeV, which is significantly lower than the GUT scale. To illustrate these features, we discuss Minimal Flavor Violation for the Standard Model augmented by sterile neutrinos. (C) 2019 The Authors. Published by Elsevier B.V.