Striking is increasing the labor cost, possibly tipping the balance.

Possibly, but I would be willing to bet the difference in labor prices abroad and in the US were greater in previous decades, and that labor prices abroad have been increasing quicker than US labor prices.

I know that with telecommunications, there are a bunch of companies here in Australia that are bringing call centres back on shore just because non-native speakers make so many mistakes with their data entry that it's not worth the cost of fixing it.