Answer: b. the power to move production to another country.
Explanation:
Multinational companies are multinational because they are present in multiple areas around the world including areas that have different levels of development.
This means that if they are negotiating with unions in developed areas like the western world, if they find that the cost of labor is more than they are willing to pay, they could move production to another less developed country where they can pay lower wages and this is a constant concern for domestic labor unions.