Workers who are taking a leave under the Family and Medical Leave Act (FMLA) expect that they will have their job waiting for them when they return to work. This isn't always the way that it happens. Some employers will terminate a worker who is on this type of leave. If you are terminated while on FMLA leave, you should find out if you can file a claim against the employer.
Employees aren't robots, so employers shouldn't expect them to be able to work every shift without having any issues. Things like illnesses, pregnancies, adoptions and sick children come up. This is where the Family and Medical Leave Act comes into the picture.