Wal-Mart is America’s biggest corporation. It’s also one of the country’s worst union busters, so it’s hardly a surprise that it engages in under-handed tactics to get its way with its workers and with America’s politicians.

But a story out of Southern California is particularly shocking.

Warehouse Workers United (WWU), a new organization for warehouse workers in the area, caught Wal-Mart actually sending a fake “reporter” to spy on a group of workers trying to organize warehouses.

At first, the spy identified herself as “Zoe Mitchell,” a USC student “interested in terrible and illegal conditions inside warehouses that move goods for Walmart.” She told warehouse workers that she was a reporter looking into their plight.

But then WWU discovered her true identity. Zoe is actually Stephanie — Stephanie Harnett of Mercury Public Affairs, a giant public relations  and lobbying firm that brags of specializing in “Latino Communications“:

For months warehouse workers have been asking to meet with Walmart. There have been many opportunities to sit down with workers: Last year the state issued more than $1 million in fines for labor violations at warehouses where workers move goods for Walmart, UCLA conducted a study about the risky working conditions inside the warehouse, Cal/OSHA issued more than 60 violations totaling more than $250,000 in Walmart-contracted warehouses and workers at a Walmart-contracted warehouse filed a class action lawsuit that documents awful working conditions including working 362 days a years with no break and no overtime. Last week when Walmart had the chance to talk about real issues affecting Latino workers in Southern California it instead sent “Zoe,” a fake reporter. A spy. Our door is open. Walmart can change this industry and create thousands of good jobs and improve the quality of life in Southern California, but first it has to come out of hiding.

Mercury is one of the fastest growing lobbying firms in the country. Recently, it merged with Clark & Weinstock, a major lobbying firm. The current partner roster features Fabian Nunez, the former Democratic Speaker of the California legislature, Romney advisors Jim Talent and Vin Weber, as well as Max Sandlin, a former Democratic congressman from Texas.

The WWU are also pointing out that Stephanie has a Twitter handle (she describes herself as a “storyteller at heart”) where she can be reached: @stephharnett. Ironically, the last Tweet she wrote was this: “RIP Ray Bradbury, the world’s greatest lover of books.” One has to wonder what Bradbury — the author of numerous books about secrecy and propaganda like Fahrenheit 451 — would think about Wal-Mart using a front group to spy on workers fighting for their rights.

UPDATE: It seems Stephanie has pulled down her Twitter account, but you can find some of her old Tweets here.

UPDATE II: We visited the offices of Mercury here in D.C. to talk to them about Harnett. The managing director, Peter Barden, repeatedly insisted that he had no information about her infiltration of WWU. He did, however, confirm for us that Wal-Mart is a client of Mercury.

UPDATE III: Wal-Mart gave this statement to Gawker: “These actions were unacceptable, misleading and wrong. Our culture of integrity is a constant at Walmart and by not properly identifying herself, this individual’s behavior was contrary to our values and the way we do business. We insist that all our vendors conduct themselves in a way that is transparent and honest and we will reinforce that expectation to help ensure this type of activity is not repeated.”