arbitrator
From Longman Business Dictionaryarbitratorar‧bi‧trat‧or /ˈɑːbətreɪtəˈɑːrbətreɪtər/ noun [countable] LAWHUMAN RESOURCESJOBa professional person whose job is to act as a judge in legal or industrial disagreementsIf we accept your claim but disagree with the amount due to you, the matter will be passed to a legally appointed arbitrator.