I suspect it's much easier for someone to sue on the claim of being unfairly discriminated against than on the claim that a particular company policy with a legitimate stated justification is an unfair labor practice.
Just because there's a justification doesn't make it an excuse to participate in anticompetitive behavior. The NLRB getting involved seems like a bigger risk than the letter of recommendation.
You've offered no facts to support what little you've said. You "suspect" some things and have been told some other things by your manager. I too have been told things by managers and suspect things myself. But I guess because it's your opinion, everyone else's opinion must be wrong.
I'm sorry for my earlier responses. I was becoming ill, didn't realize it, and that messes with my temper. One day I'll learn not to argue with people on the internet when that happens.