Continued protectionist views in America could threaten the Open Skies agreement signed this year between the EU and the US.
The warning came from Jacques Barrot, the EC transport commissioner, who has written to Mary Peters, the US transportation secretary and James Oberstar, chairman of the House transportation and infrastructure committee.
In his letter Mr Barrot outlined his fears about plans by Mr Oberstar's committee to tighten existing laws on foreign ownership of airlines in the US.
The move comes after BA's chairman Martin Broughton again described the Open Skies deal as a "bad agreement" in which the EC let go of its prize asset, entry into London Heathrow, too easily.
It also emerged that Sir Richard Branson will not travel to the States next month for the launch of his Virgin America airline because of US sensitivity over foreign ownership.
Mr Barrot said that any tightening of the law regarding foreign ownership would have a "serious impact" on the Open Skies deal.
Mr Oberstar's committee wants to ensure that only US citizens can control a US airline.
The potential clash comes a week after the UK's transport secretary Ruth Kelly said the EU would be pushing for a more liberal agreement once the new deal comes into force next March.
"The (UK) government with our European counterparts will be strongly pressing the case for further liberalisation in Washington.
"It is neither in America's nor Europe's interests for the restrictions to continue," she said.
Accor reports 8.8% revenue rise
French hotel group Accor reported an 8.8% rise in revenue for the first six months of 2007.
It total revenue from both hotels and services for the six months was 4,015m, compared with 3,690m for the same period in 2006.
Its mid- and upmarket hotels fared the best with a 14.1% rise in revenue from 1,457m to 1,663m.
Its economy hotels showed a 7.7% rise in revenue from 717m to 772m but its US economy hotels showed a 6.2% drop from 492m to 461m.
All the hotels together showed an 8.6% increase in revenue from 2,666m to 2,896m.
Accor said the hotel figures confirmed the "continuing uptrend in the European hospitality
industry cycle underway since fourth-quarter 2006."
It said growth in Europe was led by increases in both the occupancy rate (up 1.1%) and the average room rate (up 6.9%).
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