Ryanair today moved to force Aer Lingus to hold an emergency general meeting of shareholders after the company last week refused the request.
The airline, which is the biggest shareholder in Aer Lingus with 29.4 per cent of shares, issued a notice to the stock exchange today of requisition under the Companies Act and Aer Lingus's articles of association.
The statement said that in view of the recently announced 58 per cent decline in Aer Lingus interim profits, the directors "are hereby directed to take such actions as may be required to preserve the company's existing profitable Shannon-Heathrow services".
Ryanair, whose attempts to buy-out Aer Lingus have been blocked by EU competition watchdogs, initially requested an EGM following Aer Lingus's announcement last month that it would cut its Shannon to Heathrow service.
"The board of Aer Lingus has no discretion in this matter," Ryanair Chief Executive Michael O'Leary told reporters at a press conference in Dublin.
But Aer Lingus management said on Friday that the holding of an EGM would infringe Irish and EU competition law.
"Any costs of convening that EGM must be discharged by Aer Lingus and deducted from Aer Lingus directors' fees," Mr O'Leary said.
"Aer Lingus will also have to take appropriate action against the directors for failing to comply with their statutory duty."
In its notice today Ryanair also said that the meeting was necessary to "explore the €4 million per annum of additional cost reductions recently identified by the Shannon Airport Authority to enhance shareholder returns".
Aer Lingus confirmed this afternoon that it had received Ryanair's latest request, but was not commenting.
Aer Lingus chairman John Sharman said last week that Ryanair's proposed resolutions were self-serving and motivated by the airline's own commercial interests.
Mr Sharman said that in June Ryanair was ready to give up Aer Lingus Heathrow slots in an attempt to acquire control of the airline, which has since been blocked. "Its recently expressed concern in relation to these [Heathrow] slots therefore has no credibility."
The board has received legal advice saying in effect Aer Lingus would be in breach of its "fiduciary duties and, potentially, guilty of an offence under the Competition Act" if it were to convene an EGM for the purpose of the resolutions proposed by Ryanair, Mr Sharman said.
Meanwhile groups opposing Aer Lingus's move have today reacted angrily to comments by Taoiseach Bertie Ahern that the Government will not be intervening to force the airline to reverse its decision.
Mr Ahern said last night that the Government had no advance warning of Aer Lingus' "disappointing" decision to move its Heathrow connection from Shannon to Belfast.
"They made a commercial decision for commercial reasons and that's their view and they're not open to change.
"We wish they didn't make that decision but that's what they did and that's a commercial decision whether we like it or not."