  The persisting anomalous data in semileptonic B-decays point towards New
Physics models exhibiting large sources of Lepton Flavour Universality
Violation. In this work we generalise previous studies by considering
frameworks which include an enlarged set of semileptonic four-fermion operators
invariant under the SM gauge group, with New Physics affecting mainly the third
generation. We derive the low-energy effective Lagrangian including the leading
electroweak corrections, mandatory to obtain reliable predictions. As a
particularly interesting case, we analyse the scenario where the dominant New
Physics effects are encoded in the Wilson coefficient C_9, as favoured by
global fit analyses of b -> s data. We find that also in this case the
stringent experimental bounds on Z-pole observables and tau decays challenge a
simultaneous explanation of charged and neutral-current non-standard data.
