  Charged-pion decay offers many opportunities to study Lorentz violation.
Using an effective field theory approach, we study Lorentz violation in the
lepton, W-boson, and quark sectors and derive the differential pion-decay rate,
including muon polarization. Using coordinate redefinitions we are able to
relate the first-generation quark sector, in which no bounds were previously
reported, to the lepton and W-boson sector. This facilitates a tractable
calculation, enabling us to place bounds on the level of $10^{-4}$ on
first-generation quark parameters. Our expression for the pion-decay rate can
be used to constrain Lorentz violation in future experiments.
