The history of the unionization of graduate student-workers dates back to the early 1970s. Given recent economic conditions, more and more graduate students are incurring debt and facing an increasingly uncertain job market, and there has been a sharp rise in unionization–twenty campuses have unionized since 2000. The UCs became fully unionized in 1999 with the United Auto Workers. The UAW is also the union of the University of Massachusetts and University of Washington university systems.
A full history of the UAW is available here: http://uaw2865history.wordpress.com/