In 1965, the football team was promoted to the Segunda División Argentina for the first time. The team has played there for many years, alternating with periods in the second division. Unión's supporters are called "unionistas", "tatengues", while the squad is usually nicknamed "El Tate". The colours of the club consist of red and white vertical stripes.
In 1979 Unión played the final matches of the Nacional championship, but lost at the hands of River Plate, because the goal scored by River in the first match (with a final score of 1–1) ended up in an average over Union according to the away goals rule applied to that tournament.