The Techno Union was formed at least 300 years prior to the Battle of Coruscant.
In the lead up to the Clone Wars, the Techno Union was among the major corporate powers who pledged loyalty to the Separatist Alliance, with its Foreman Wat Tambor being given a spot on the Separatist leadership council. The Techno Union designed many of the droids used by the Separatist Droid Army, including the B1 and B2 Battle Droids.
Despite their alliance with the Separatists, the Techno Union claimed neutrality in the Clone Wars and even had representation with their Senator Gume Saam in the Galactic Senate.
After the Clone Wars ended and the Republic was reformed into the Galactic Empire, the Techno Union was annexed into the new order.