My employer is saying I can get in trouble for calling in even with a note?

Today I called into work today as I had an eye appointment and got my eyes dilated (didn’t know that would happen). I am part time at a restaurant that won’t be named (Jesus Chicken). They are saying I need to find coverage and could be given disciplinary action if no one comes in. Is that allowed? I have a note from my doctor excusing me from work.