The term 'Plumber's Union' refers to a labor union that represents plumbers and other related tradespeople. The two crossword solutions for this term are TEE and ELL, which are abbreviations for the International Association of Plumbing and Mechanical Officials (IAPMO) and the United Association of Journeymen and Apprentices of the Plumbing and Pipe Fitting Industry (UA), respectively. These two organizations are the two main unions that represent plumbers and other related tradespeople in the United States.