Small firm intern told “no overtime for you”

I started interning at a small firm and am really enjoying the environment. However, when I first got there I was informed I was not eligible for overtime because I am a grad student. I am still being paid at an hourly rate.  Even if it's not legal I'm hesitant to bring it up because they may not want me to work over 40 hours if they have to pay out the overtime, which could end up costing me money rather than making it, and I don't want to make a bad impression. I received other offers that tried to entice me with the opportunity to work overtime and make a lot of money. This doesn't seem legal to me from everything I've read. Thoughts on how to proceed?