Oh yikes, I'm so sorry.
Yes, it's legal, but there are limitations for an IEP student. Repost on the special education board and the experts over there can explain.
It doesn't sound like it would likely be much help though. Have you met with the teacher and principal to find out exactly what occured? You will want to reconvene the IEP team to discuss preventative measures. Does your son have a one on one aide? That can be helpful for many kids.