Human resource scheduling | Human Resource Management homework help

Scheduling manager implimented preference base bidding for employees which caused hostile environment because their schedule changes every week. If customer service employees schedules changes everyweek  drastic  are there any laws against contract union base employees they can file if their schedule bidding changes every week.  Are there laws or regulation employees can causes grievance against manager, or not Explain?  Is there Ways they file or not? if there are ways names some laws if not explain how resolve hostile environment