This organization, one of my favorites, has been around for a decade and a half (it used to be called the Interfaith Committee for Worker Justice) and is based in Chicago, a long-time center of labor activity, and indeed labor-and-religion activity (think Monsignor Jack Egan, Monsignor George Higgins, and the Chicago Jewish Labor Committee). Interfaith Worker Justice (IWJ) has branches and chapters all over, including in the Oakland/ SanFrancisco Bay Area, where I was involved with it, and where there is now also an affiliated group called Seminarians for Worker Justice.
On Labor Day Weekend IWJ also has a "Labor in the Pulpit" (and yes, in Muslim and Jewish, not just Christian, congregations) event,* which I think is how I first encountered this group.
*******I see it's now "Labor in the Pulpits, Labor on the Bimah, Labor in the Minbar."
Have a look. You need to know this group exists. Have a look at the resources and information in the left-hand column. You'll notice items related to immigration, the Katrina aftermath, Congress and the minimum wage, and the recent IWJ national conference.
The dreaded Wikipedia is pretty accurate on the subject of IWJ and has some interesting information.
But do go to the primary source.