Fire all of them, void the contracts and hire non-union replacements (I wish)
Do what Wisconsin did: pass right-to-work for public employees, and forbid public employers from taking union dues out of paychecks. A large percentage of WI school teachers quit their unions.
...it would be astounding at the number of the present teachers who would sign up.
It would cleanse the gene pool too. The bad teachers would go away since their protection racket was dismantled.
If Deadfish would just fire all the union teachers, the disruption would last for one or two days, whereas the "strike" scenario will last for weeks, and cause untold misery and hostility.