US politicians yesterday moved to ratchet up the pressure on the EU over charging carriers for carbon emitting during flights in and out of the bloc, although Brussels pledged to stand firm on the regulation.

Representatives of both parties used a Senate Commerce Committee hearing to condemn the scheme, which US airlines claim violates international treaties, will cost them more than $3bn by the end of the decade, and may force up ticket prices for travellers.

Transport secretary Ray LaHood, who last year wrote a joint letter with Secretary of State Hillary Clinton urging the EU to rethink the regulation, said the US government “strongly opposes the EU scheme on both legal and policy grounds,” and vowed appropriate action would be taken should Brussels fail to repeal the measure.

The US is considering whether to ban its airlines from participating in EU emissions trading, raising the prospect of a transatlantic trade war. LaHood said no decision had been made on potential steps, but raised the possibility of the US filing a formal complaint to the United Nations.

The EU says it will save 185 million tonnes of CO2 through the directive, which came into force at the beginning of the year after a court case brought by US airlines was dismissed. But the US, along with many other nations, including China, Russia and India, maintains unilateral action is the wrong way to tackle aviation emissions, which currently account for three per cent of the global total – as much as the UK’s overall output – and are projected to quadruple by 2050.

They would prefer a global deal, but 10 years of talks at the International Civil Aviation Organisation (ICAO) have failed to produce such a solution.

“The European Union acted because it believes it needed to make a bold effort to reduce greenhouse gas emissions and I understand why they did so,” said panel chairman and Democrat senator Jay Rockefeller at yesterday’s hearing.

“But, I believe that their unilateral action is likely not sustainable by international law. I support the goals, but I have to oppose the action.”

However, Jos Delbeke, director general for climate action at the European Commission, insisted Brussels would not back down on the policy, which officials estimate will add only €3 to €5 to the price of a long-haul ticket.

“There is no prospect of suspending the EU legislation,” Delbeke said in a statement at the hearing. “There have been some exceptionally high estimates of costs, which are unfounded.”

He added the EU would welcome a global approach and could modify its emissions trading system to incorporate a negotiated solution as long as the market-based measures proposed were similarly stringent, covered all airlines and included specific goals.

Delbeke was supported by Annie Petsonk, international counsel at campaign group Environmental Defense Fund (EDF), who highlighted analyses by MIT and others that have found additional costs per trip were likely to be about half the price of an in-flight beer and that airlines might even profit from the law.

She said the EU regulations were “modest, effective, and reasonable,” could create jobs in the US without significant costs to the industry and intrude into US sovereignty “no more than similar US laws intrude into the sovereignty of other countries”.

However, as long as the row continues without resolution carriers will be concerned business travellers could turn to alternatives such as rail or videoconferencing.