[header] How to legally require employees to get a flu shot [title] Identify if your employees are " at will. [step] " in every state but montana, employees are " at will " unless you have changed the relationship. You can fire " at will " employees for any legal reason, at any time. 
However, you may have changed the " at will " status in the following ways : [substeps] Your employees are unionized and you agreed to a collective bargaining agreement. In this situation, the terms of the bargaining agreement will control whether you can require flu shots.