Did you balk at it? In my experience car dealers tend to both appeal to authority as a first line of defense ("It's out of my control. That fee is mandatory."), yet also will do anything they can to close a deal. I'd be curious if walking out would get it removed.
A forced arbitration clause was included by my realtor in all the paperwork I filled out when buying a house last year. I didn't sign that page and nobody brought it up again.