"Be very careful who you let into your neighborhood," Sandra Carpenter, a former Wal-Mart grocery manager from Maryland, warned New Yorkers considering whether to bring Wal-Mart to their town. "They will promise you everything under the sun," she said at a recent anti-Wal-Mart rally outside New York City Hall, "but at the end of the day, they will take it all back."

Wal-Mart's high-profile effort to expand into some major urban markets has suddenly cast a spotlight on the experiences of Wal-Mart workers like Carpenter and launched a battle that both Wal-Mart and the United Food and Commercial Workers (UFCW), the union that represents grocery workers, badly need to win.