There are regulations about making claims about anything as a cure or proven treatment when there is no actual proof. That doesn't mean clinics etc can't use it, just that they have to be careful about making unproven claims about it. Obviously there also has to be a safety factor in what is being given.

So offering IV infusions of Vit C is likely not the problem here...but making unproven claims about it likely led to this action?
At least that is the way I read that article, which is a little short on actual information though!