Players are heading toward a "legal dispute" with the Premiership Rugby to stop the league from imposing permanent salary cuts following a salary cap reduction, the Rugby Players Association (RPA) said on Wednesday.
Premiership clubs voted unanimously on Monday to cut the salary cap by £1.4 million from the 2021-22 season.
In March, several Premiership clubs negotiated 25% pay reductions with players, including recently relegated Saracens, to protect finances during the coronavirus pandemic.
"The RPA is opposed to permanent cuts for our members," RPA chairman and Harlequins prop Mark Lambert said in a statement.
"The RPA have been working diligently over the last 12 weeks to seek to avoid a repeat of the damaging situation the game found itself in when the clubs imposed temporary wage cuts on a unilateral basis in mid-March.
"This latest situation could have been entirely avoided with a collaborative and transparent approach and we now find ourselves heading towards a significant legal dispute unless meaningful and genuine dialogue takes place urgently.
"From the outset of this crisis there has been an absolute disregard for the players and the values of the game. Players at some clubs are now being served with ultimatums and being put under undue pressure to sign amended contracts through the manufactured deadline of June 18. To be clear, this is a totally unacceptable way to operate."
The Premiership rugby salary cap, which stood at £6.4m this season, will be reduced to £5m from the 2021-22 season. The number of marquee player dispensations, players who are exempt from the salary cap, will also be reduced to one player per team from the 2022-23 season, except for where a club has two existing marquee players.
All existing contracts that carry into the 2021-22 season will be counted into the salary cap at 75% of their value.
"Our clubs have taken these difficult steps as part of a range of measures to weather the significant financial impact of the coronavirus pandemic," Premiership rugby chief executive Darren Childs said on Monday.
"The ambition for the future of the game remains unchanged, and as we look beyond the immediate crisis we know that Premiership Rugby has huge potential to bring people together and will grow as a sport with the players, clubs and all stakeholders sharing in that future."