  The success of the quantum level predictions of the Standard Model on the $Z$
boson properties, on $\mw$ and on $\mt$, which makes use of the muon lifetime
as an input, implies a stringent constraint on new physics contributions to the
$V-A$ charged-current interactions among leptons. Observed unitarity of the CKM
matrix elements then implies constraints on non-standard contributions to the
lepton-quark charged-current interactions. By using the recent electroweak data
as inputs, we find the 95%~CL limits for the corresponding contact
interactions: $\Lambda_{CC,+}^{\ell\ell}>7.5$ TeV and
$\Lambda_{CC,-}^{\ell\ell}>10.2$ TeV for the purely leptonic terms, and
$\Lambda_{CC,+}^{\ell q}>5.8$ TeV and $\Lambda_{CC,-}^{\ell q}>10.1$~TeV for
the lepton-quark contact interactions.
