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At least in the US, almost all full-time orchestras are union shops with the American Federation of Musicians. The first stop for major issues should not be with management's HR, but with the union local and the union steward for the orchestra. Most of these orchestras also have an Orchestra Committee made up of musicians, and it is this committee's job to help as well. And most of the largest orchestras do have an HR rep.

HR is there to protect management. The union is there to protect employees as a collective. Individual results may vary.