Global symmetries in the antifield formalism

In this paper, two things are done. First, it is shown that any global symmetry of a gauge-invariant theory can be extended to the ghosts and the antifields so as to leave invariant the solution of the master equation (before gauge fixing). Second, it is proved that the incorporation of the rigid symmetries to the solution of the master equation through the introduction of a constant ghost for each global symmetry can be obstructed already at the classical level whenever the theory possesses higher order conservation laws. Explicit examples are given.