Abstract: We study the isospin-violating J/psi -> Lambda(Sigma) over bar (0)eta reaction, recently measured by the BESIII collaboration, by considering the dominant terms involving (Sigma) over bar (0) and pairs of pseudoscalar-baryon particles that together form an SU(3) singlet and can therefore couple to the . We then allow these pairs to undergo final-state interaction to produce J/psi the final . We find that the relevant original channels are and , and that the incomplete cancellation of KN and K Xi and terms involving charged and neutral particles, owing to their different masses, is responsible for the reaction. With this mechanism, we find good agreement with the three experimental mass distributions.