That sounds pretty unfair to me. And perhaps even illegal. But is probably isn't.
Thing is, people who started one month after you now get a higher salary, because there were performance reviews before they started at your company. Then, that would mean salaries have been raised throughout your entire firm, otherwise they'd be earning the same amount as you do. And that would logically lead to the conclusion that you should get a raise too, right?
Hmm, come think of it. You've probably signed a contract for a certain salary. That would explain, otherwise I don't understand. But that could be my ignorance.