European supporters groups on Wednesday said plans by the Spanish and Italian football federations to host league matches overseas were "absurd".
Spain's LaLiga has agreed to move a game between champions Barcelona and Villarreal to Miami, Florida, on 20 December.
The Serie A encounter between AC Milan and Como is due to be staged in Perth, Australia, on 6 February to avoid a clash with the Winter Olympics opening ceremony at Milan's San Siro stadium.
While various Super Cups are staged abroad these two fixtures will represent a first for European leagues.
"The concept of flying players, staff, fans, and others across oceans for a 'home' game is absurd, unaffordable, and environmentally irresponsible," the Football Supporters Europe (FSE) wrote in a statement signed by 423 groups from 25 countries.
The FSE, claiming to represent "million of football fans", fears that if Uefa backs the idea on 11 September it will open "a Pandora's box with unpredictable and irreversible consequences".
"Every club, every national team, every fan base globally would be at risk of seeing the team they love taken away from them, relocated to another part of the world, for one game or more," the FSE warned.
The Spanish and Italian Super Cups are already held in Saudi Arabia, after previous editions in China, Morocco, Qatar and Libya as governing bodies seek to cash in on the global reach of the beautiful game.
LaLiga has been trying for years to host games in the United States, home of its commercial partner Relevent Sports.
Serie A and LaLiga are following the example set by major American leagues, the NFL and especially the NBA, which has relocated regular-season matches since 1990 to Japan and since 2013 to Europe, and has already scheduled six games in Berlin, London, Manchester and Paris over the next three seasons.
Football's world governing body Fifa has shifted its hitherto opposition to relocating matches, with a 'working group' launched in May to revise their rules.
On Wednesday, Uefa president Aleksander Ceferin told Politico: "We are not happy (about the relocation projects), but we have little room for manoeuvre legally if the two federations agree."
The issue has now become political, with the intervention of the European Commissioner for Sports, Glenn Micallef.
"Relocating competitions abroad is not an innovation, it's a betrayal," he said last week on X.
In Spain LaLiga's plan has come under fire not least from the captains of Barcelona and Villarreal who have criticised "the lack of dialogue and information" from LaLiga.