can a stepfather discipline children?

I am left in charge of 3 children at night while my wife is at school.(2 step). Last night I asked to see step sons homework, reviewed it and asked if there was more-he said no and went back to playing XBOX live with his friends. This morning he was working on homework before school with his mother who had caught him trying to finish it before school. I got mad at being lied to about this, this is not the first that he has done this, or that I have received heat about this. I said to him that I am pulling the XBOX without consulting my wife. She got very angry with me saying I am the stepfather and have no right to discipline. This was also done in front of son which I dont agree with. She had already pulled the plug and I did not know this. I feel that if he is left in my charge I have the right to discipine and she should not have yelled at me in front of him about this. She says a stepfather has no rights on this, and I have to consult her first.