The liberalisation of the air corridor was expected by EU ministers to be sealed at a June meeting, but the issue is becoming increasingly controversial in the US, where Congress has approved a non-binding measure that will delay proposals to relax foreign ownership of US airlines. Over 160 Congress members have sponsored a bill to completely veto any rule change on ownership.

According to government sources, there were strong indications last week following an EC meeting that the open skies agreement would be approved at a June meeting of ministers.

However, European Commission air transport director, Daniel Calleja, said last week that unless ownership rules are relaxed, EU ministers would have to "re-evaluate" the situation and there would be "no agreement" on open skies. A respected New York-based airline consultant, Bob Mann, said it is "likely" an open skies agreement will not be reached until next year.

An Aer Lingus spokeswoman said on Friday that the carrier has contingency plans in the event a deal is not struck. She said the plan put in place includes increasing frequencies on existing US routes and also on new services such as that to Dubai.

But any doubts over the open skies deal will almost certainly have a negative impact on the value of Aer Lingus to investors. Aer Lingus has predicated much of its projected growth on being able to expand its US longhaul services. While the carrier could instead refocus on routes to Asia and South Africa, such a strategy would be seen as a higher risk to investors, one Dublin analyst said last week.

Transport minister Martin Cullen is expected to present proposals at a cabinet meeting this Tuesday for the sale of Aer Lingus. It could be valued at as much as 800m.