Union suit

A union suit is a type of one-piece long underwear. Created in Utica, New York, it originated as women's wear during the 19th-century United States clothing reform efforts, as an alternative to constricting garments, and soon gained popularity among men as well. The first union suit was patented in 1868 as "emancipation union under flannel." Traditionally made of red flannel with long arms and long legs, it buttoned up the front and had a button-up flap in the rear covering the buttocks (colloquially known as the "access hatch", "drop seat", "fireman's flap", and other names), allowing the wearer to eliminate bodily waste without removing the garment. Depending on the size, some union suits can have a dozen buttons on the front to be fastened through buttonholes from the neck down to the groin area.

The garment remained in common use in North America into the 20th century. As its popularity waned, it became chiefly working men's wear, increasingly replaced by two-piece long underwear, also known as "long johns". It was not uncommon until the mid-20th century for rural men to wear the same union suit continuously all week, or even all winter. Normally, no other type of underwear was worn with it.