The Dallas Cowboys and Washington Redskins appealed the decision by the NFL which was that the two clubs were penalized for overspending in the 2010 uncapped year. The appeal was rejected and the Cowboys had to accept the penalties which resulted in losing $10 million of salary cap funds which was not that bad compared to the Redskins who lost $36 million.
Now there is new coming out the NFLPA was "strong-armed" into accepting the deal for the Redskins and Cowboys, this according to Yahoo's Jason Cole:
...the NFL was essentially able to strong-arm the NFLPA into accepting collusion in exchange for concessions on the salary cap.
Basically the NFLPA chose to accept the penalties for the Cowboys and Redskins in exchange for a higher salary cap, and if there was no deal then the salary cap would have at $113 million and that would have affected a lot of players.
So, the NFLPA had to make a choice which would have affected every team or just a pair of teams, and they chose to agree to the penalties for the Cowboys and Redskins to benefit the rest of the league with a higher salary cap.