Is it legal?

If you are pregnant and you have a doctors note saying that you have a certain restriction. And your workplace tells you too bad if you can't do that restriction they're going to fire you, and keep scheduling you to unload the truck by yourself. When before they would at least give you help. Everyone else gets help but your being punished for having a drs note.  And they tell you that you cant do anything else till the whole truck is unloaded (take 2hrs with two ppl) and they are only giving you 3 hours or a write up is that legal? She also ripped up the drs note. I am asking because my cousin works and she is 34 weeks and she told me this morning this happened to her. She works in the untied states in Iowa. Is there anything she can do?