Barcelona have been warned by the AFE (Spanish Players' Union) over their threat made to forward Ousmane Dembele.
It follows comments from Barca's sporting director Mateu Alemany on Thursday that "we have told him he must leave the club as soon as possible", after no agreement could be found on a new contract.
Barca boss Xavi Hernandez feels cheated by the Frenchman and the player was handed a final warning by the coach on Wednesday in what appeared to be a transfer ultimatum.
That preceded the club excluding the forward - who is out of contract at the Camp Nou in June - from the squad travelling to Athletic Bilbao in Thursday night's Copa del Rey clash.
The Catalan club have already completed the signing of Ferran Torres from Manchester City this month in what appears to be a direct replacement for Dembele in the squad.
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Yet the demand from Barca's sporting director Alemany that the player "must leave the club as soon as possible" has drawn the wrath of the AFE, who say that such a claim is in breach of the player's contract.
The union believe that such comments infringe on the player's "labour rights" which come into force when a contract between the two parties is signed.
An AFE statement reads: "In relation to the situation experienced by the FC Barcelona footballer Ousmane Dembele, the Association of Spanish Footballers wants to express the following:
"The AFE considers that the signing of an employment contract as a professional soccer player obliges him to provide his services on behalf of the club following the instructions provided to him.
"On the other hand, the club is obliged to pay the agreed wages and allow the provision of services under the same conditions as the rest of his teammates, without there being any type of discrimination or pressure for the athlete to waive their labour rights.
"We understand that the renewal of a contract requires the agreement of the will of both parties. Said agreement of wills must be issued freely without there being external conditions that limit or restrict the freedom of contracting of the professional soccer player.
"It is true that a professional footballer does not have the right to be lined up or even called up for every match, but rather to be treated under the same conditions as his teammates and to be able to play those matches.
"But if this circumstance could be understood as pressure to bend their will, and public statements are also made acknowledging this type of pressure, we would be facing an illegal action by the company.
"AFE considers that not reaching an agreement to renew an employment contract does not imply a labour breach, so it cannot have any consequence for the provision of services.
"The non-alignment of a footballer for a period of time without any injury, illness or physical impediment, supposes a devaluation of his image and his sports cache that will negatively affect his future contracts.
"At AFE we want this situation to be resolved without the worker's rights being violated and we remind you that AFE is available to any footballer who may see their labour rights violated as a worker."
Dembele is out of contract at the Camp Nou in June and the club are now hopeful of moving the player on this month in order to avoid losing him as a free agent and saving on his wages.
Manchester United, Chelsea and Paris Saint-Germain have been among the clubs linked with a possible move for the Frenchman.
Barca paid £105million - in a deal rising to a potential £135m - to sign Dembele from Borussia Dortmund in 2017 in a transfer that has become symbolic of the club's reckless transfer policy.