Too late, it's already happened. The FBI has already used OnStar equipment to monitor what was going on inside a car.
A judge slapped them down for doing it, not for constitutional reasons, but for 'contractual interference'. Apparently when they do this, your little buttons don't work anymore, and a judge didn't think that the FBI could come and change your tire or unlock your doors for you.
Just one more reason not to buy a GM car. Between their quality and this, no wonder their sales are slipping.