Recently, Buchholz and Fredenhagen proposed a formulation for interacting quantum field theory (QFT) using the C*-algebra generated by unitaries interpreted as local S-matrices and by relations corresponding to causality and dynamics; the latter implemented by the unitary Schwinger-Dyson equation. Unitary Master Ward Identity is a natural generalization of the unitary Schwinger-Dyson equation to the situation, where non-trivial local symmetries are present. This talk is based on recent results in collaboration with Brunetti, Duetsch, Fredenhagen and Hawkins.