It's not merely the unions. I would put government regulation (fed,state,county,city) and taxation (state,county, city) that drives companies out.
My breakdown for California (& I know at least one is closing in CA)
45% regulations and the cost to keep records
30% state and local taxes
25% unions and associated costs to having workers on your teat for life.
Regulations drove the textile manufacturing out of the USA to China and India, not the unions.