The current article on MlB.com says that the MLBPA tried to prevent disclosure of parts of the arbitrator's opinion, but a federal judge blocked that, and indicated there was no reason the opinion shouldn't be public. After that, A-Rod's lawyer apparently put the opinion out in full.

His suit against the MLBPA is intended to maximize his slim chances of overturning the suspension by attacking all angles in the process. But the MLBPA's reply suggests they're not happy with their inclusion.