The Professional Footballers' Association have threatened to serve the English Football League with another arbitration over squad size limits for the 2021-22 campaign in an open letter to all EFL clubs and players.
In February, an independent panel unanimously confirmed that the introduction of a salary cap without agreement from the Premier League, the FA and the PFA was in breach of the legally binding Professional Football Negotiating and Consultative Committee (PFNCC) constitution and it was subsequently withdrawn.
Caps had been voted through by third and fourth-tier clubs in August last year and were set at £2.5million per club in League One and £1.5million per club in League Two.
In addition to the now withdrawn salary cap, a squad limit size was implemented and is set to limit teams in League One and League Two next season to only 20 players.
While the Championship clubs will be able to select 25 players for their 46-game campaign, it will be a smaller number for sides in the bottom two tiers of the EFL.
The PFA sent their open letter to the EFL, their clubs and players on Wednesday, which read: "Following the logic of the panel's decision in the salary caps case, the PFA expected the EFL to remove the squad size limits (25 for the Championship, and as from next season, 20 for Leagues One and Two) because these limits were also introduced without consultation or the agreement required from the members of the PFNCC.
"Unfortunately, the EFL is refusing to withdraw the squad size limits. Frustrating as this is, unless another solution can be found, the PFA must now therefore consider commencing a further arbitration claim and/or bringing other legal claims.
"This would cause a further needless waste of legal costs, money that ultimately the clubs themselves have to pay if the EFL is again unsuccessful."