“Bound” means required or obligated. It indicates that the company has a legal responsibility to involve the union in important decisions because of a special agreement. Hope this helps!

Bound there means to be under legal obligation

In this sentence, "bound" means obligated or required. The company is obligated by a special agreement to include the union in important decisions.

The word "bound" in isolation doesn't have this exact meaning. It's a bit of a metaphor since this use of "bound" literally means to be tied up with rope or some similar sort of material. "To be (legally, morally or ethically) bound" is a phrase that carries the meaning "to be required or obligated." You can be "(legally) bound to" perform an action or meet an obligation, or you can be "(legally) bound by" a law or a contract. In this context, the "special agreement" is a legally binding contract that probably specifies some sort of penalty if the company doesn't abide by the agreement.