Is it legal for an employer to force certain individuals in a group to change their scheduled hours?

I work in a group of approx. 50 associates, many of whom begin work between the hours of 5 and 7 AM. Recently, a new manager was hired and has decided she does not want only certain individuals (specifically 4) to work these hours and is changing them to begin at a later start time (8 AM). However, the other individuals will be allowed to keep their regularly scheduled shifts. There has been turmoil in the past between us and this manager, and it seems us not agreeing to work more than 40 hours per wk without overtime pay (she offers "comp" time only, meaning if you work 42 hours in 1 wk eventually you will get 2 hours off in the future in lieu of extra pay) has made her try and punish the select few. Is it legal to do so, especially when certain individuals have reasons for working early such as living 50 miles away and trying to miss traffic?