  We show that in the background field method (BFM) quantization of Yang-Mills
theory the dependence of the vertex functional on the background field is
controlled by a canonical transformation w.r.t. the Batalin-Vilkovisky bracket,
naturally associated with the BRST symmetry of the theory. Since it only relies
on the Slavnov-Taylor identity of the model, this result holds both in
perturbation theory and in the non-perturbative regime. It provides a general
consistent framework for the systematic implementation of the BFM in
non-perturbative approaches to QCD, like e.g. those based on the
Schwinger-Dyson equations or the lattice, in the presence of topologically
non-trivial background configurations. The analysis is carried out in an
arbitrary (background) R_\xi-gauge.
