If there is no employment contract (including a union agreement) covering your branch or  position(s), then your employer is pretty much free to set different work rules, hours, compensation, etc. for different branches--it may not be fair but it is legal. You only recourse would  be if you could show that the discrepancy is due to illegal discrimation; for example, if your branch is heavily African American (or Hispanic, or Asian, etc.) and the other branches are not, and the pay discrepancy is due to discrimination against a protected group or category. The categories protected under federal law are race, sex, religion, disability, and age over 40. However, again, without a contract or discrimination, employees can treat different offices or personnel differently.