PFA Scotland chief executive Fraser Wishart has warned Charles Green that he cannot pick and choose elements of employment law and claimed that Rangers players were becoming increasingly frustrated at a lack of information over their futures.
Wishart has rejected Green's claim that players would be in "breach of contract" if they exercised their right to leave Ibrox amid a change of corporate structure.
In a statement, Wishart said: "Should the players wish to transfer across to the newco, TUPE ensures that they do so on their existing contractual terms."
Green is poised to push ahead with a £5.5million deal to buy the club's assets and form a new club, which would need to apply for membership of the Scottish Premier League and be excluded from Europe for three years.
Rangers administrator Paul Clark has said their lawyers had been in talks with their PFA counterparts and had different interpretations of the the Transfer of Undertakings (Protection of Employment) (TUPE) regulations.
The union believe players could leave for free and Wishart has now raised the prospect of legal action should any who wish to do so be prevented from leaving Ibrox by the football authorities.
Wishart continued: "TUPE affords every employee the statutory right to object to the transfer; employers cannot select which parts of TUPE they wish to apply.
"If a player wishes to object to being transferred his contract of employment would immediately come to an end leaving him with no contract, no dismissal and no right to compensation from either oldco or newco.
"Both the club and the player are then free from their contractual obligations."