Why do some do more work than their co-workers and act like they are getting an award when we are paid same and there really is no incentive to really do that?

I work in a unionized call center where we all make the same amount of money at different “steps” of time being there and all make the same at final step. There are no incentives to really go “above and beyond” to take more calls. When we process our work, it is actually very technical, so management cares more about error rate.

I have a coworker who knocks herself out taking 20 to 30 or more calls every day when our average is 14 to16.

It bothers me at times because management always seems to try and take things away or add more stats when our union contract is up for renewal. And, I'm concerned because they might get an idea to use her as their “poster person” to try and change that stat when our work is hard enough. It seems like we have to fight tooth and nail for every little thing we get.

Also, I can say that everyone pitches in and does their work; I don't know anyone who is a slouch about it.

I'm curious what others make of this?

Edit I realized I should add: She has a higher error rate and is almost always close to being warned.