A labor union representing National Football League players called Tuesday on its clients to better prepare themselves ahead of another potential high-stakes legal battle with the league.

The two sides signed a 10-year collective bargaining agreement in 2011 after an acrimonious antitrust fight that led to a five-month lockout of NFL players. With the expiration of that deal now looming on the horizon, executives with the NFL Players Association are urging their gridiron rank-and-file to begin making financial preparations to help head off another work stoppage. And the Washington, D.C.-based union also has more than a few high-powered lawyers at its disposal.

Five Am Law 100 firms billed the NFLPA for legal fees during its most recent fiscal year, according to an annual LM-2 filing made by the union with the U.S. Department of Labor before the Memorial Day weekend. Winston & Strawn, which took in nearly $4.5 million from the NFLPA during its last fiscal year, once again took the top spot with more than $1.91 million in billings for the organization in the one-year period between March 1, 2016 and Feb. 28, 2017.