You could sue the attorney who represented you for malpractice, but when trying cases the attorney has discretion over witnesses and questions in his best legal judgment and you would have to prove that he was negligent in his actions. You will also have to prove that had the witnesses been allowed to testify or had other witnesses been asked the questions as prior to the hearing that the outcome would have likely been different. As far as suing the union, they only had a duty to provide you the representation with the attorney and technically he was the agent of the union and you could sue them if you could prove that they were negligent in selecting an attorney to represent you.
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