[vharuck]

Take the National Basketball Players Association as an example. They represent NBA players and collectively bargained for a minimum wage, benefits, and processes to address grievances with management. NBA players aren't all paid the same, and they don't have identical terms in their contracts. The union sets the floor.

[abdullahkhalids]

For a more down to earth example, my graduate school student union also only negotiated the floor of pay and benefits. The compensation for graduate students varied easily by 50% over this floor, even students in the same department.