Walmart is a strong supporter of comprehensive immigration reform, aka amnesty and probably wouldn't cooperate on immigration raids with the Department of Homeland Security. Why bother? Back in 2005, after they were caught using illegal labor, they got a slap on the wrist: a fine equivalent to their revenue in a fifteen minute period.

Despite that, one or more groups - perhaps originating with the Georgia Latino Alliance for Human Rights have sent viral text messages urging a boycott of Wal Mart, even claiming that they'd let ICE into their stores to arrest illegal aliens on March 20, the day before yet another illegal immigration march (Snopes, snopes.com/politics/immigration/walmart.asp). The company, of course, claims that this isn't true. And, the US Hispanic Chamber of Commerce weighs in on their side, "Laud[ing] Walmart's Collaborative Approach in Support of Comprehensive Immigration Reform" (link).