What do I do in this situation?

I know these girls who are literally ADDICTED to the card game President. At first, I thought it was just a game hat hey liked and so played a lo, but hey are OBSESSED with it. They're 14 BTW and there are about 5-10 of them. They play it at lunch, at recess, during class, on the bus, at home, and in their spare time. It's been going on for about a month now, and I'm actually getting worried. It's all they ever do. I've been thinking about an intervention, but that isn't practical...