The International Air Transport Association estimates airlines will lose at least $US200 million per day in revenues as a result of the Iceland volcanic ash disruption.
Airspace across most of Europe is closed because of the ash, from an eruption on Wednesday.
IATA said its members would also lose further money as a result of expensive contingency plans.
The association said the estimate is "initial and conservative".
The BBC reports shares in major European airlines fell on Friday as the volcanic ash cloud spread across Europe.
British Airways saw its share price fall by 3.3%. Air France-KLM lost 3.4%, and Lufthansa was down 4.1%.