More than 20 nations opposed to the scheme grouped together in a "coalition of the unwilling". They last met in Moscow, when they agreed possible retaliatory measures and said they would meet again in Saudi Arabia, although a date has not been confirmed.
"You cannot enforce laws outside your sovereign area. Its implications are huge," Indian Civil Aviation Minister Ajit Singh told Reuters last week.
"Now you are talking about aviation, tomorrow you will talk about shipping. ICAO is there, these things will have be done in a multilateral basis."
The EU’s highest court, the EU Court of Justice, ruled in December last year that the law was valid and did not breach international treaties. It also agreed with the Commission that the ETS was a market-based mechanism, not a tax.
The cost of carbon allowances on the EU ETS has fallen to record lows, pressured by oversupply following economic recession.
On Tuesday, carbon prices were trading at below 7 euros a ton - far below levels needed to spur low carbon investment.
Hedegaard said in April that the Commission was reviewing its carbon-auctioning timetable to try to reduce oversupply in the market.
She expected news on the review before the Commission breaks for its August recess, with a legal decision expected before the end of the year.
Changing the auctioning timetable to limit supply in the nearer term - or "backloading" - was a relatively quick solution, but other options under discussion, including setting aside allowances, could take longer.
"We should not expect backloading will do the whole trick. That’s a first step, which does not take a lot of time. The more structural things are a more complicated process," Hedegaard said. - Reuters