  A class of topological field theories like the $BF$ model and Chern-Simons
theory, when quantized in the Landau gauge, enjoys the property of invariance
under a vector supersymmetry, which is responsible for their finiteness. We
introduce a new type of gauge fixing which makes these theories invariant under
an extended $BRS$ symmetry, containing a new type of field, the ghost of
diffeomorphisms. The presence of such an extension is naturally related to the
vector supersymmetry discussed before.
