Premiership rugby stars could go on strike over contractual issues arising from the league's expected confirmation of a reduction of next season's salary cap by up to 25%.
Rugby Players' Association chairman and Harlequins prop Mark Lambert says some of his members are being "strong-armed" into accepting reduced contracts as a result, and could not rule out taking the ultimate sanction.
Clubs have started returning to non-contact training this week having reportedly struck a unanimous deal to reduce the salary cap to help ease the financial burden of the pandemic.
Lambert, who has made 239 appearances for Quins, said: "We very much see it (a strike) in any walk of life as the last action, and something you would look to avoid for the benefit of all stakeholders, because it is an extreme move.
"But it's difficult for us to entirely rule out any options when we're in the current situation where we've got members with existing, fixed-term contracts in some senses essentially being strong-armed into thinking they have no choice but to sign an inferior contract."
Lambert said that while the RPA fully appreciates the need to face up to what he described as the "unprecedented financial challenges", he could not condone the "absolute disregard" with which players have been treated during the process.
In an earlier statement, he said: "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 18 June.
"To be clear, this is a totally unacceptable way to operate. Players are the lifeblood of the game and should be treated with respect. Players should not engage with this approach.
"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."
Premiership players have already undertaken 25 per cent wage cuts during the coronavirus lockdown, and face the prospect of the reductions being made permanent under the new arrangement.
The salary cap reduction was agreed partly as a consequence of a review by Lord Myners, commissioned by Premiership Rugby, in the wake of the breaches by Saracens.
Myners' review found the current level of the cap to be broadly unsustainable, with only one Premiership club recording a profit last season, and called for tougher sanctions for clubs breaching the limit in future.