Huge swaths of US citizens are staunchly anti-union. They get fed these stories about unions being the reason that American car companies are failing and Detroit has gone to shit, because apparently they're being bled dry by the union that demands they pay $60/hour for starting unskilled laborers and there's a strike if the drinking fountains are more than 20 steps apart. Teachers unions and teacher strikes in particular are held up as some kind of example of shitty teachers who don't do any work but can't be fired and demand to be paid doctors' wages despite only working 180 days a year.

Realistically, the teachers' union in the area I live is fighting for things like the teachers being allowed to use the bathroom between classes, or restricting the pointless meetings and trainings during planning periods so they have at least 2 days a week where their meager 40-50 minute planning period isn't wasted.