From Newsweek (HT BoingBoing):

Wal-Mart is Mexicos largest private-sector employer in the nationtoday, with nearly 150,000 local residents on its payroll. Anadditional 19,000 youngsters between the ages of 14 and 16 work afterschool in hundreds of Wal-Mart stores, mostly as grocery baggers,throughout Mexicoand none of them receives a red cent in wages orfringe benefits. The company doesnt try to conceal this practice: its62 Superama supermarkets display blue signs with white letters thattell shoppers: OUR VOLUNTEER PACKERS COLLECT NO SALARY, ONLY THEGRATUITY THAT YOU GIVE THEM. SUPERAMA THANKS YOU FOR YOURUNDERSTANDING. The use of unsalaried youths is legal in Mexico becausethe kids are said to be volunteering their services to Wal-Mart andare therefore not subject to the requirements and regulations thatwould otherwise apply under the countrys labor laws. But someofficials south of the U.S. border nonetheless view the practice asregrettable, if not downright exploitative. These kids should receivea salary, says Labor Undersecretary Patricia Espinosa Torres. If youask me, I dont think these kids should be working, but there arecultural and social circumstances [in Mexico] rooted in poverty andscarcity.