equity?

[eakirchhoff]

So myself and 5 others were all promoted to Temporary supervisor on the same day, all with understanding that after 90 days we would get permanent status. 3 people got offers and the other 3 were told our paperwork got held up. Over 4 months later we are still waiting for the paperwork and now have been told that instead of gaining full salary like the others we will be ramped up. They claim that our hire dates will be retro'd back to our 91st day in the position. My question is does an employer have the right to treat one group of people differently when all were hired for the same position, all at the same time?