Ryanair has yet to decide whether to back a deal to end a long-running pension dispute at Aer Lingus that is seen as key to the airline's valuation.
Ryanair is the largest shareholder in Aer Lingus.
The pension scheme, which employees at Aer Lingus share with other aviation industry workers, has a deficit of over €700m compared to Aer Lingus' market capitalisation of €880m.
The shareholder vote on the proposed one-off €191m payment is the last major obstacle to a resolution.
Aer Lingus' share price briefly climbed 10% when union members voted to back the deal earlier this month.
"We haven't made any decision yet. We will consider the EGM proposals and make a decision based on that," Ryanair's chief executive Michael O'Leary told Reuters.
Ryanair owns 30% of Aer Lingus, but is currently appealing an order by Britain's Competition and Markets Authority (CMA) for it to cut its stake to 5%.
Mr O'Leary said he had not yet decided whether to ask for CMA permission to vote in the December 10 extraordinary general meeting.
But he said he still opposed in principle the approach Aer Lingus management were taking, saying the deal was "just another roll over" by management to staff demands.
Analysts say the pensions issue has complicated attempts in recent years by Ryanair and the Government, which owns a 25% stake in Aer Lingus, to sell off their shareholdings.
An Aer Lingus spokesman this month said no major shareholders had indicated how they would vote at the EGM.