The source is that hotbed of liberal activists, the University of Alabama.
http://usnews.msnbc.msn.com/_news/2012/02/01/10290742-cost-of-alabama-immigration-law-disputed
I think the real gem is that of the jobs vacated by people fleeing the state, only 9% of them have been filled by unemployed people in Alabama. Does that mean they are now at full exmployment, that the unemployed are unqualified for the jobs, or that they don't want to do the work?