Did you sign up or are you being voluntold?
If you are not on the list, then "they" are supposed to utilize ARCs 1st, list RCAs 2nd and non-list RCAs third.
If you are on the list, the MOU states that it doesn't go by office.
You may or may not have a grievance (talk to your union rep and go up the line until you get an answer), but it were me, I'd be filing mileage reimbursement.
(edit: RCA = relief carriers. because someone will hone in on the language in mou lol)