First, you need to approach him and ask him the reasons for breaking the rules. You can then warn him that if he repeats that again he will receive a severe punishment. You need to also talk to him in a polite way as this will help you find out the main reason of breaking the rules.
All kids will push their luck with their parents but if you're worried about a power struggle I'm sorry to say you're looking at it the wrong way and will lose. You're the adult. You set the rules and take the actions needed to enforce them
Teens are a constant power struggle because they are struggling with a new sense of independance. Be the adult and put your foot down. Make very clear rules, make your expectations clear and enforce them consistently. Grounding, restrictions and taking away electronics are the best ways. I had a co-worker once who cut the cord of her teens TV once when her teen defied her and refused to turn it off when told. Removal of computers, phones, ipods, etc is quite good punishment for most teens.
A part of loving a child is enforcing rules to teach them that there are consequences for bad choices or actions. You should love your children enough to be willing to go through the hassles of teaching them life's lessons before they're out there on their own.