American companies can always find somebody somewhere in the world who is willing to do a particular job at a lower wage than the person currently doing that job. But American companies are supposed to hire from a pool of workers that includes only Americans and legal immigrants. If it were legal to do so, many companies would get rid of all of their American workers and replace them with cheap imported foreign workers.
In some cases, it IS legal. It's called "outsourcing" and that results in PRChina jobs.
It's also called Labor Arbitrage.