"Backed by the captains of the La Liga clubs, AFE opposes playing a league game outside of Spain," a statement from the union read.
"The captains of every team met on Thursday to discuss the request, as announced by the RFEF earlier in August, for a game to be played outside of the country, which was submitted to UEFA and FIFA.
"AFE requested a detailed report from the league in order to inform the players of the situation and hear their opinions. In its response, the league only informed us of the progress of the authorisation process.
"In view of this situation, given the lack of dialogue and information provided, the initiation of a project promoted by La Liga and approved without any information by the RFEF is disrespectful to the players, as it involves changes at a sporting level in addition to travel outside the country as workers within the framework of a domestic league."
The statement continued: "We are united. We want respect and transparency. With this message, AFE demands that the Spanish institutions involved provide all the information on a project that would alter the competition.
"This is something that requires dialogue, negotiation and prior agreement with all stakeholders and, fundamentally, with the main players, which are us."