Gomer: I see it this way. If you wanted to have a different break location on a specific day (say to take your break at home or whatever) mgt MAY allow you to do so, but they don't HAVE to let you.
Your break locations are set on the form in your route book and are supposed to be agreed on mutually between mgt and the carrier. If your nutjob PM wants to change your break locations against your wishes, that's a unilateral change in working conditions and you might could fight it on that basis.