The International Air Transport Association (IATA) says airlines could lose more than $1.7bn in revenue, six days after the initial eruption of the volcano in Iceland started and grounded flights across Europe.
Airlines lost an estimated $400m per day for a three-day period from 17-19 April when the crisis reached its peak.
IATA's director general and CEO Giovanni Bisignani said at the worst, the crisis impacted 29% of global aviation and affected 1.2 million passengers a day.
Bisignani recommended that governments relax rules on take-off and landing slot allocations to reflect the extraordinary nature of the crisis.
The IATA has also asked for bans on night flights to be relaxed to allow carriers every opportunity to meet stranded passenger's travel arrangements as soon as possible, as well as address unfair passenger care regulations.
Bisignani said that more than five mid-size and small European airlines risk bankruptcy after the volcanic ash cloud halted traffic.
The EC is considering allowing EU governments permission to provide aid or compensation to airlines affected by the recent shutdown of airspace.