Most "discrimination" is perfectly legal--employers can, and inevitably do, prefer or favor one employee over another. The only time it is illegal is when it is based on a protected characteristic--that is, for example, when the differential treatment is based on an employee's race, sex, religion, disability, or age over 40. (That's under federal law; some states add a few other protected categories, like sexual orientation or national origin.) In the case you describe, if the difference in treatment is not based on a protected characteristic, it would be legal. It may be unfair, but the law does not enforce fairness.