Here's an excellent article about an alleged unlawful English-Only policy at Macy's in Minnesota where workers are claiming they were threatened with termination for speaking with each other in their native Somali language while they sorted merchandise in a basement closed off from the customers. Macy's denies having an English-Only policy.
Read more about the story here: http://minnesota.publicradio.org/display/web/2008/09/22/somali_macys/
Read the Equal Employment Opportunity Commission's guidance on English-Only policies: English-only rules
Source: Macy's Case Highlights Confusion Over English-Only Rules (NPR), accessed Sept. 25, 08