  We find that, at order alpha_s, the partial width of Z^0 to heavy flavors
receives a power correction from a novel QCD mechanism, which is not suppressed
by inverse powers of M_Z, but only by two unknown O(\lambdaqcd/m) constants.
The hadronic W width also receives a similar correction. These parameters may
be fitted from the global electroweak analysis, and consequently the Standard
Model predictions of various electroweak observables will be updated. This new
mechanism is of no help to reconcile the discrepancy in b forward-backward
asymmetry. We also point out the implication of this mechanism to heavy flavor
production in other collider experiments.
