It doesnt matter whether it's Walmart or the next company. Point is they're getting hired.
People come to the States for work. Companies employ them, despite the risk of breaking the law, because they ask for much less money than the country's own workforce.
Now, if you force the companies employing them to pay Jose the same wage that Joe gets, the incentive the company had to emply Jose in the first place is gone, and Joe doesnt have to fear unfair competition. If Jose actually does a better job than Joe, then all credit to him and Joe should work harder.
Now, this is tackling the problem at the roots instead of milling about the muddy waters trying to stop the effects. The reason this most likely is never going to happen is because a government will try to protect it's domestic labour market from overflooding immigrants willing to work harder. In other words, it's being selfish. Why is it being selfish? Because the country's higher rate of living needs more money to sustain itself, thus opening the gates to a whole new pool of labourers is suicide in their eyes. Because they don't wanna see Cindy, who is doing a 2nd rate job, get replaced by Augusta, who does a 1st rate job. Now Jack, who also does a 1st rate job, won't get replaced by a second rate Miguel, because Joe is doing fine in the first place.
Harsh, but true. And there's some sense in it from the government/people's perspective. But I plead for a free labour market. If you get out-worked by someone else, work harder. Period.
EDIT: This is more in general than about the bill.