Can a person get fired for being too slow?

Like in e-commerce for example. My uph is decent I think but I'm just wondering. Like can low uph be used as a reason to let someone go? It seems like discrimination because what if a person is doing their best and their uph is low? What if they struggle working too fast or are out of shape or something? What if they have some kind of disability? But they are otherwise a good employee (show up to work on time, nice to team members and customers, detail-oriented, etc.). I've seen other departments working quickly too and I'm curious if someone could be fired for not being as fast as the department desires.