South American football chiefs have asked world governing body Fifa to suspend its ban on international games being played at high altitude.
High altitude an unfair advantage? Views are divided
At a meeting in Paraguay, the federation said more time was needed to study the issue.
Fifa decided last month to ban matches over 2,500m (8,200ft) above sea level, citing concerns about players' health.
Andean nations Bolivia, Colombia, Peru and Ecuador, where many matches take place at altitude, reacted with fury.
It is simply inconceivable, they say, to prevent international club matches and World Cup qualifiers from being played in cities such as La Paz, Quito and Bogota.
A Fifa spokesman told the BBC that the ban remains and there would be no further developments on this issue until Fifa's next meeting on 27 June.
The South American federation, known by its Spanish acronym Conmebol, can block the Fifa ban, but member nations are far from united in their stance.
HIGH ALTITUDE CITIES
Bolivia: La Paz - 3,600m (11,811ft)
Ecuador: Quito - 2,800m (9,186ft)
Colombia: Bogota - 2,640m (8,661ft)
Peru: Cuzco - 3,500m (11,482ft)
Bolivian President Evo Morales has been leading the Andean campaign, playing football at altitude as often as he can to show that it is not, contrary to Fifa's view, dangerous to players' health.
Earlier this week, he reached new heights playing at 6,000m (19,700 ft) above sea level in Bolivia, although the game only lasted about 15 minutes.
Mr Morales arrived in Asuncion on Friday to lobby Conmebol members.
"We're here in the name of the Bolivian people to appeal to sporting conscience, to sporting justice," he said.
Football, he added, "makes us forget our problems, economic, social and political".
Fifa spokesman Andreas Herren told the BBC that the ban remained in place.
He insisted that the measure was adopted because of concerns about the dangers of playing at high altitude and the fact that the constraints of the international footballing calendar give teams little time to acclimatise.
There are accusations that footballing giants Argentina and Brazil proposed the ban in the first place, the BBC's Daniel Schweimler reports from the meeting in Asuncion.
Bolivian protesters take their argument to Conmebol
They have been unhappy at playing World Cup qualifying matches at high altitude, including proposals for games in the Peruvian city of Cuzco in the Andes mountains.
Playing sport in conditions of high altitude places heavy demands on the body, forcing the heart to work harder.
Andean medical experts have argued that playing at high altitude does not cause major problems.
However doctors from low-altitude nations say that if teams have less than a week to adapt, players can suffer oxygen deprivation, causing headache, nausea and fatigue.
The Copa America competition, which involves the 12 major footballing nations in the region, kicks off in Venezuela on 26 June and delegates will be hoping to be able to present some kind of united front.
They may hope to thrash out a compromise solution to send to Fifa headquarters in Zurich, correspondents say.