I had not heard anything regarding treatment of workers who produce stuff FOR Walmart. Most of the Walmart is evil stories that I've heard are based on information related to the actual retail stores.
There's a couple different ones going around. They are supposed to have a lot of arcane employment policies and procedures that favor the corporation and not the employees. There are a number of lawsuits pending against them.
It is not unusual for Walmart employees to be told they have to work a certain number of hours "off the clock" in order to keep their jobs. They are putting in full or overtime hours, but only clock in for a part-time number of hours, thus saving corporate from having to provide them insurance benefits due to full time workers.
If a worker gets injured during one of these "off the clock" times (back injuries from lifting or other injuries from being struck by falling merchandise for example) they do NOT qualify for Workman's Comp to which they would otherwise be entitled.
I recently admitted a Walmart employee who DID qualify for the insurance benefits ... even had an official Blue Cross ID card with the patient's name and plan numbers ... the Blue Cross provider had NO record of the policy ever having been placed into effect. (I asked this person about the off-the-clock policy and it was confirmed)
I've heard other stuff as well ... that the corporate no fraternization rules state that employees cannot "form relationships" (i.e., date each other) and if a marriage DOES ultimately result, the female employee is the one who is fired.
THE anti-Walmart Site
Myths and Truths About Walmart
Walmart Forces Workers to Work Off The Clock
5,000 Lawsuits Pending Against Walmart
Class Action Suit for Gender Discrimination
Walmart Found Guilty in Unpaid Overtime Suit
Oh, heck ... Just google it; there are tons of examples.
I don't as a general rule shop in Walmart, just in case you were wondering. There was an attempt many years ago to keep Walmart out of the part of Montgomery County in which I live ... it was unsuccessful. A (regular sized, not super) Walmart opened in East Norriton last year.