Simple. Because that directly and negatively impacts the function of the company, economically and productively. It also falls under economic terrorism because they are taking a political action as their basis.
The intent, ultimately, is to circumvent the law and force the company to hire only union and return to forcing union employees to pay up...at threat of lowering produvtivity of said employees and thuscorporate income.
Is it economic terrorism when a corporation fires a 1000 Americans and hire a bunch of H1B’s or ships the jobs to a bunch of low wage Chinamen?