Apparently FIFA, the Fédération Internationale de Football Association, has relaxed the restrictions on high-altitude soccer games for international matches from 2500 to 3000 meters. This will now allow for a couple previously banned cities in Colombia and Ecuador to host international games.

Interesting problem: players who routinely practice in higher altitudes will have more endurance when playing against other teams at lower altitudes. I don't think that constitutes an unfair advantage, though; there are always players that are better than others, and this is just one possible manifestation of that.