The term "union suit" has largely passed out of usage, as has the suit itself, but if you've heard the term and wondered what a union suit looked like, you now know, as this poster provides an excellent example.
A union suit was a type of one-piece long underwear, usually knitted, typically worn by men in the late 19th and early 20th centuries. They wore their union suits under their everyday clothes in the winter for extra insulation against the cold. It was called a union suit because the top and bottom were united in one piece.
This World War II lithograph published by the Office of War Information in 1943 shows an empty union suit holding a sign telling Americans that fuel was needed for the war effort and implies that it was therefore each citizen's duty to conserve it. One way to do this, as the poster says, is to dress warmly indoors.
The poster goes on to remind citizens to avoid colds.
Check out all our WWI and WWII vintage posters to get an interesting historical perspective on how our country met the challenges that these wars posed to the folks at home. You'll come away with some interesting observations of your own.