There is a legal question. It would have to be litigated to be resolved, though. The argument is that when RHEL threatens to cut off future business, they are placing a restriction on redistribution. RHEL would argue that it's a restriction on future business, not on current redistribution, but who can say what a court would make of that distinction.
It's true that RHEL does not have to continue a business relationship in general, but the point here is that they need to follow the GPL when making relevant business decisions.