Is it Discrimination?

I am an asian man, the only one in the business unit, 50 yrs old, have worked for a fortune 10 company for the last 10 years. Last Thursday 12/1 my most recent supervisor gave me my review and said I was in the Below Expectation category. It has been made clear that merger and consolidation activity will seek to shed the low performers to which I have never been in my entire employment with the company. I have extensive documentation most recently and accolades along with the first half of the year review which corroborates this. When I went to present my performance data to refute the rating, I was basically told "too late" it has been booked in October and wont be changed! All I have written in my review is "need to become a more effective manager" yet I show in the very same review major accomplishments on an enterprize wide scale, some of which even made it into world wide business news, solid dollar savings, and soft dollar efficiency improvements. Others who are at the same position level as me have lesser contributions, I am only guessing that they were not ranked as lowly as me as I have heard no grousing. Do I have some type of recourse before the other shoe drops? Or am I at the mercy of having to live with a sub-par rating, and always being tagged as the 1st to be sacrificed? thanks
ATT