older employees because companies have pay insurance premiums 3x that of a 21 year old
women employees because of pregnancy and maternity leave and burden of caring for children makes them less able to commit more of their time
disabled employees because their insurance premiums are higher and they're viewed as less able to commit more of their time or work hard
any employee on medical leave as disability insurance premiums become higher and cost of having an employee not available when sick is a buzzkill, i've known of employees fired when in the hospital or on leave
minority employees because they are not seen as cultural fits and are less cooperative than their counterparts and a legal employment hassle