Ask Jolie on the Michigan thread. This is her forte.
I'll PM you
There's a list of schools with certificates here, see "Specialized Programs" on right-hand side-http://lawprofessors.typepad.com/laborprof_blog/Cornell, Illinois, Wisconsin, UPenn, Hofstra, Hamline, St. John's, Northeastern, WVU and Buffalo also have good labor classes/faculty. I'm going into labor law myself (2L interning at a union now), so PM me if you have any more questions.