It depends. If some employees are receiving less favorable treatment based on discriminatory factors such as their race, religion, disability (age over 40), national origin and the like, then it is illegal. That having been said, preferential treatment based on any other reason is legal. The fact is that not all employees need be treated the same or even fairly. In an "at will" work setting, employers can set the conditions of the workplace much as they see fit. This holds true so long as a company's action does not violate the terms of any union agreement/collective bargaining agreement or employment contract.