> it was just a dress code, how will you treat me if I bring up a more serious issue?

They did bring up the dress code issue to their managers, and it was dismissed. Petitioning it is a level above that, and while I agree that firing them is a bit much, it doesn't mean they can't take feedback necessarily. It sounds like they would still be receptive if you bring up a more serious issue in the proper way (i.e. talking to your manager).