Most people do not go to school and strive to become a plumber. If you finish your degree you will be so far ahead of the plumbers around you, you can rise to the top fast. Plumbing is a decent trade but I wouldn't tell my kids to stay in school and become a plumber. You can always do plumbing, but not a degree.
If you do go that route the union is great but you can also move up much faster and learn more in a quality open shop then test out and organzise in later. The classes are a must though.