'Employers who hire aliens not authorized to work in the United States are subject to fines ranging from $250 to $10,000 for each unauthorized alien. Additionally, employers who demonstrate a pattern of knowingly hiring unauthorized aliens may face up to a six-month prison term.'
http://www.law.com/jsp/tx/PubArticleTX.jsp?id=1097686231889
As I read the story, this thread isn't about unauthorized aliens, but then again, most threads these days end up there, so maybe you're on to something.
If there were any undocumented workers from outside our country's borders, they might have been used as box clerks or were on the cleaning crews.
The cashier positions, meat cutters, produce and even stock crews need to be trained and in some cases require some experience before handling money, food or interacting with the public.