Ground sets the price, and they are hardly the only courier service that uses contractors. But they are definitely the largest.
A lot of you guys don't seem to understand how the contractor model works, so I'll explain it on a scale that makes it easier to understand. All of us here are familiar with UPS Freight. They are a unionized LTL carrier. Here in Canada, however, UPS Freight (and Overnite before them) contracts their services to a Canadian non-union carrier called Canada Cartage. UPS sets the prices to the customer, but they pay Canada Cartage to be their representative in the market. Canada Cartage, in turn, paints the trucks dedicated to the contract UPS brown, complete with logos, and the trailers are similarly UPS gray if they are not UPS' own trailers. Canada Cartage employees doing pickups and deliveries is these UPS-look trucks likewise wear a UPSF uniform.
Why is that done this way? Because UPS has no interest in the expensive process of expanding into the Canadian market and hiring employees. It's cheaper to contract the operation out to a local carrier willing to represent them. As part of the contract, UPS expects the contractor to represent UPS to the customer. As far as the customer is concerned, the truck that picks up the freight is a UPS truck, and the branding is important to UPS.
This does not make the Canada Cartage employees who represent UPS employees of UPS. They are paid by Canada Cartage, not UPS. And they are made fully aware that their job is to represent UPS to UPS' customers. The case is exactly the same with FedEx Ground after 2011, just on a smaller scale.