In the work presented here, we have studied the impact of right handed neutrinos, which are introduced to account for the evidence of neutrino masses, on charged lepton flavour violating observables. In particular, we have focused on the loop induced decays of the Z boson into two leptons of different flavour. We have performed a numerical study of the rates predicted for these processes within the Inverse Seesaw model, specifically considering scenarios where $ \mu -e $ transitions are suppressed. Our conclusion, after comparison with the most relevant experimental constraints, is that branching ratios as large as $ 10^{-7} $ can be predicted in the $ \tau -\mu $ or $ \tau -e $ channels, together with heavy neutrinos having masses of the TeV order. Such rates could be accessible at next generation colliders.