Tennessee voters have approved a change to the state Constitution that reinforces the state’s existing law freeing workers from being required to pay union dues. Tennessee has had a law prohibiting the requirement on the books since 1947, and the outcome of Tuesday’s referendum doesn’t change how the existing law works. But Republican politicians and businesses wanted a constitutional amendment to make it more difficult to weaken or overturn the law, known to its supporters as a “right-to-work” law.