There are several ways to prove discrimination. A very common method is to focus on disparate treatment. Bob commits some offense at work. He is treated differently than Pedro regarding the same offense. If nothing can explain why Bob gets treated differently, then one might conclude that he was treated differently due to his ethnic origin. This is a difficult way to show discrimination. Mike Maslanka discusses the challenges when he discusses a recent case, Lee v. Kansas City Southern Railway Co. I hear this all the time. The "other" employees are treated better because they are the boss’ favorites. They come in late and nothing happens to them.
The challenge is to show that Bob and Pedro are good comparators. Do they have the same boss? Are they in the same department? If Bob was disciplined for the same offense, but Pedro was not, is the offense truly the same? Do Pedro and Bob have the same responsibilities, training, experience? All these are factors. What the Lee decision helps with is it shows that if Bob ad Pedro have the same second level supervisor, then yes, they might be good comparative employees. That is, if the boss’ boss approves the discipline, then yes, they might be good comparators. So, yes, if Bob gets disciplined for an offense for which Pedro was not disciplined, then that different treatment might constitute evidence of discrimination.