When did Kentucky ban strikes?

With the possibility of a teachers' strike looming in Kentucky, several media sources have said that strikes are illegal in this state.

When did this happen? Evidently, this provision is included in the unconstitutional "right-to-work" law that passed last year. Why was this swept under the rug?

It should be a moot point, since the right to strike is of course constitutionally protected. The U.S. Constitution outweighs some Matt Bevin diktat any day.