Employees need to prove they suffered some sort of "adverse job action" (firing, demotion, worse job conditions, etc.) to file a discrimination lawsuit. But variations in work schedules don't necessarily amount to an adverse action.
That's true even if an employee's altered schedule results in fewer overtime hours and, therefore, a smaller paycheck. To claim adverse action, the employment decision must produce a material employment disadvantage.
Recent case: John Baucom worked as an assistant manager at a convenience store. The 68-year-old man suffers from chronic back pain and a heart problem. When his hours were cut so he no longer earned much overtime, he suspected age discrimination and sued.
The court threw out his case, concluding the schedule change was likely caused by the nature of the convenience-store business. It also concluded that losing a few hours of overtime pay doesn't amount to retaliation or evidence of age discrimination. (Baucom v. Holiday Companies, No. 05-1393, 8th Cir., 2005)
Final tip: Your organization will have an even easier time proving that schedule changes aren't "adverse actions" if your industry experiences seasonal shifts in employee staffing needs or economic conditions sometimes require you to reduce work hours. Also, be aware that the U.S. Surpreme Court will soon rule on what defines an "adverse action."