Uh, Jody? Hello?
They can set up whatever terms of payment they want subject to existing contracts. The only real argument here is the amount of notification required. The devil in this case is only in the details. The contract can specify weekly payment or payment ten years in advance. The only caveat being the possibility of no actual current contract and that there is an existing tradition of payment otherwise. Which, in no way prevents the issuance of a new contract, with different terms, subject to acceptence or rejection by the other party. Rejection constituting an agreement to discontinue the use of facilities and services.
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.