Well given that a union at least initially isn't part of the formal company structures almost by definition then there needs to be some process of recognition t

Well given that a union at least initially isn't part of the formal company structures almost by definition then there needs to be some process of recognition that yes this organisation that claims to represent my employees does in fact represent my employees. But in this case, the union is already established and recognized by the acquired employer. MS (or any other acquiring entity) shouldn’t be allowed to ignore an existing employer-labor relationship. If that were true, any time a company unionized, the stockholders could just continually buy itself with another shell company and terminate the union relationship.