I am not sure, but I think it means that the players decertifed the union and because of that, they can sue the NFL.
From ESPN:
By dissolving and announcing it no longer represents the players in collective bargaining, the union cleared the way for class-action lawsuits against the NFL, which opted out of the CBA in 2008. The antitrust suit -- forever to be known as Brady et al vs. National Football League et al -- attacked the league's policies on the draft, salary cap and free-agent restrictions such as franchise-player tags.
Invoking the Sherman Act, a federal antitrust statute from 1890 that limits monopolies and restrictions on commerce, the players are seeking triple the amount of damages they've incurred. That means the stakes here could be in the hundreds of millions.