Aer Lingus has said that its rival Ryanair's "poison-pill" shareholding is deterring potential investors.
The chief executive, Christoph Mueller, has claimed that bosses of European carriers had cited Ryanair's 29pc ownership of the business as an obstacle to any deal.
"A minority shareholding from an alliance partner is restricted by Ryanair," he said. "The shareholding works as a poison pill."
The flag carrier is 25pc owned by the Irish Government with its employees owning a further 14pc.
Potential investment partners in the loss-making airline include British Airways and US operator United Airlines, with whom it has strategic alliances. But Mueller said a corporate tie-up with another airline was impossible while Ryanair stays on the share register.
"The fact that Ryanair is a shareholder is a limiting factor in attracting other airline shareholders in the framework of a global alliance," he added.
Aer Lingus described itself as "Ireland's civilised airline" as it unveiled a plan to position itself midway between no-frills Ryanair and high-end airlines such as British Airways.
Shares in the company rose as the chief executive told investors in London of plans for a new business model that some analysts compared with that of Easyjet, Europe's second-biggest low-cost airline.