It is much harder to ask an algorithm about it's reasoning than a person's.

"Joe, why did you fire Carla?"

"She was late to work every other day and spent all day on her phone"

"HR-bot 5000, why did you fire Carla?"

"Weights indices 59738, 837, and 28836 added to over 0.67, yielding a score of only .85, which is below the firing threshold"

Certainly you could look at the input data and try to convince a jury that her performance wasn't acceptable but you can't prove that is why the AI fired her.