Vacation Time Discrimination

I work for a large company that recently combined two offices. One office has about 30 employees and the other about 20. Each office used to cover a specific geographical area but due to daily fluctuations in work load the company thought it would be better combine the areas so that work could be distributed more effectively. So now 50 employees cover one large area and report to each office depending on which area there assigned to that day. Our vacation requests for the year are due in by February. Prior to the merger each office was allowed to have a max of 3 employees off on any one day. But now we have been informed that although we are considered one geographical office the employees that previously reported to (office 1) are allowed the same 3 employees off but the employees that previously reported to (office 2) are only allowed 2 employees off per day. Like I said, now that we are combined there is no difference between the employees that used to report to office 1 and those that reported to office 2. I guess discrimination is a harsh term to use but I just can't think of another more suitable term. Is this company policy legal or ethical?