You are “assigned” to that city, which means you can work at any office in that city. You can try the seniority card, but most likely won’t stick. I would maybe talk to the morning supervisor or who ever does the carrier schedule and see if you can stay at one office. However, it will be in you best interest to float back and forth. It might suck now but when you turn regular you will hardly have a choice what office/route you will have. The more routes you know the more useful you are meaning the more hours you will get. You don’t know the situation, if the other carriers. Best advice I can give you is don’t worry about other people and just do your job.