Manufacturing workers are competing "invisibly" with foreign workers, in that they often sell (indirectly) to the same markets, buy the same supplies, etc.

Foreign manufacturing workers often work in terrible conditions for low pay.

There are a couple possible reactions to this:

1) The bleeding-heart approach: "That's horrible that those foreign workers are stuck like that! And it makes it harder for our workers to compete! We must stop foreign sweatshops!" But often if you talk to those foreign workers, they'll say it was that or prostitution.

2) (mostly discredited, but) "If lazy American workers are getting outcompeted by foreigners, so much the worse for them. This is sink or swim, boys. Welcome to the market." This is not constructive, but see its more defensible version (3) below.

3) "That's awesome that foreigners are willing to do shit work for shit pay. Let's buy their cheap stuff and use the money we save to buy their factories too. MURIKA."

If we view work as just "crappy stuff we have to do to get material goods," then 3) is sound. But if it's an arena of life that can improve the human being, then 3) is not sound.