Collective Bargaining Unit refers to the group of employees that are directly represented by a Union. In the case of the GEU it refers to all graduate Teaching Assistants at MSU as state labor laws deny graduate Research Assistants, Fellows, and Teaching Exempt the collective bargaining rights afforded other public employees.
Public Employment Relations Act (Section 1, part E-1-iii): "An individual serving as a graduate student research assistant or in an equivalent position ... is not a public employee entitled to representation or collective bargaining rights under this act."