The Spanish Footballers' Association (AFE) remains in opposition to the LaLiga game between Villarreal and Barcelona being played in Miami in December.
AFE president David Aganzo said players cannot support the proposals given the lack of information provided by the league so far, adding that he cannot guarantee the fixture will go ahead at the Hard Rock Stadium.
Aganzo had hoped to hold a meeting with LaLiga chief Javier Tebas, the captains of the 20 clubs in the Spanish top flight and the two teams involved, Barça and Villarreal, this week, but it proved impossible to get everyone together at the same time.
"Tuesday was [supposed to be] the meeting with Tebas and the clubs," Aganzo said. "We wanted some transparency and respect towards the players.
"More than just taking a game to another country, we wanted to know if the collective bargaining agreement was being fulfilled, the details surrounding the journey, the working conditions ... we want information from LaLiga.
"If it's as special as LaLiga say, why is no other club celebrating it other than Barcelona and Villarreal? I have not seen any statements celebrating it.
"I can't guarantee it will go ahead. It's the players that play these games. Football is improving, but the conditions have to as well. We have to protect the players."
LaLiga countered Aganzo by releasing a statement saying they could not attend Tuesday's meeting but had proposed three other dates.
The AFE stressed the urgency of meeting immediately, saying that all the dates offered by LaLiga came too late, at a time when tickets would already have been sold for the game in Miami.
It is unclear what steps the AFE could take next. In theory, they don't have to support the game for it to go ahead, but Aganzo said he has spoken with political parties about subsequent actions, although he added the union "don't want to ruin everything."
Aganzo also stated one of the concerns is that moving a league fixture to the United States distorts the competition, given Barça get to play an away game in a neutral venue.
"Of course it does," he added. "The players also think that. Villarreal have a better chance at home. Outside Spain, the top clubs have much more fans. It will be as if Barça are at home."
Barça midfielder Frenkie de Jong has also said he understands why other clubs would be unhappy about the advantage his team could get, while Real Madrid midfielder Dani Ceballos said Wednesday it will "adulterate" the competition.
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Madrid have been one of the biggest critics of the game, saying it will "give an undue sporting advantage" to the teams involved and "sets an unacceptable precedent."
LaLiga have been trying to relocate a game to the U.S. since 2017, but plans accelerated this month when European football governing body UEFA said it had approved two requests for games to be played on foreign soil, the other from Italian sides AC Milan and Como to play in Perth, Australia, in February.
UEFA said it was in "clear opposition" to the idea of playing domestic league games outside of their native countries but cited FIFA's vague framework and regulations when confirming it had accepted the proposals "exceptionally."
The league subsequently announced Villarreal's fixture against Barça would be played in Miami on Dec. 20.