Enterprise Association of Steamfitters Local 638 of the United Association was chartered in 1884 under the Knights of Labor as Enterprise Assembly #3189. In 1914 the Enterprise Assembly affiliated with the United Association as the Enterprise Association of Steam, Hot Water Hydraulic, Sprinkler, Pneumatic Tube, Ice Machine and General Pipe Fitters of New York and Vicinity Local 638 and the Progress Association of Steam, Hot Water and General Pipe Fitters Helpers of New York and Vicinity Local 639. At the same time, a trade line agreement was drafted which established jurisdiction between the Steamfitter and Plumber, commonly referred to as the 1914 agreement.

Today, Steamfitters Local 638 maintains jurisdiction over all general pipe fitting in New York City, including all five boroughs and all of Long Island, Nassau and Suffolk Counties and is a combination local union representing the Construction Branch and the Metal Trades Service Branch. On April 14, 2022 Enterprise Association of Steamfitters Local 638 was 137 years old.