In standard QFT, each term in the perturbative expansion for a gauge theory is not necessarily gauge-invariant. Only the whole sum of Feynman diagrams is guaranteed so.
However, at least for QED, there have been attempts to do the perturbative expansion solely in terms of gauge invariant quantities, cf. "QED : A Proof of Renormalizability" by Joel Feldman etc...
I wonder if there have been any attempt for the non-Abelian Yang-Mills theory yet?