Random insurance question

I just graduated, and I got a job at a private clinic. It is not affiliated with any medical system, but is partners with the pharmacy I used to work at. I just got all my benefits paperwork. I think this sounds kind of weird, but this is the first I've had insurance on my own, so I'm wondering if this is more common than I think. One of my letters says this:

"In an effort to maximize the benefits available and minimize out-of-pocket expenses, you are strongly encouraged NOT to use hospitals in the --- Health System for your healthcare needs... So, to help keep our health care costs down this year and in future years, --- Health Plan will assess a 5% fee on the net discounted price to all plan members who choose to utilize the --- Health system. Any fees paid by a plan member would not apply to the deductible and/or co-insurance limits."

Can they seriously do that? I could understand that if I worked for a hospital system, I should see physicians in that system, etc, and that out-of-network places are higher. But my company is not affiliated with any system at all, and this is an in-network health system according to the insurance.

Maybe I'm just peeved because my physician for 3 years is in this hospital system, so I either find a new doctor (even though mine is technically in network), or pay an extra 5% that doesn't actually go towards anything.