In this work, we develop a Lagrangian reduction theory for covariant field theories
with gauge symmetries. These symmetries are modeled by a Lie group fiber bundle
acting fiberwisely on a configuration bundle. In order to reduce the variational principle,
we utilize generalized principal connections, a type of Ehresmann connections that are
equivariant by the fiberwise action. After obtaining the reduced equations, we give the
reconstruction condition and we relate the vertical reduced equation with the Noether
theorem. Lastly, we illustrate the theory with several examples, including the classical
case (Lagrange–Poincaré reduction), Electromagnetism, symmetry-breaking and non-
Abelian gauge theories.