Do I have the right to restrict visitation if I feel my child is in danger with my ex?

I have custody of my 6 year old son. His father gets him every weekend. My son had this week off school, so I let his dad take him for a few more days than just the weekend. I received a phone call from his dad's new girlfriend stating that I needed to come get my son because she and my ex got into a fight. My ex threw a laptop computer down the stairs as well as yelling at her. This all happened in front of 3 children (my son and the girlfriend's two kids.) They argue all the time and I don't feel that it is a safe environment for my son to be in.