The Irish Airline Pilots' Association (IALPA) is shortly due to release the results of a ballot which will determine whether Aer Lingus pilots are in favour of industrial action.
The most recent vote comes after a first electronic ballot was completed last week, showing that 98% of respondents were supportive of strikes. Ninety-eight percent of eligible pilots voted.
Aer Lingus nonetheless contested the reliability of the electronic ballot, citing concerns about "statutory requirements for secrecy and the provisions of the IALPA constitution".
In response, IALPA decided to run a paper vote, judging it more efficient that bringing the matter to court.
Voting began on Friday in Cork and Dublin and is finishing on Monday morning.
On Friday, Aer Lingus' Chief Corporate Affairs Officer Donal Moriarty also suggested that the airline was concerned about the timeline of the new vote.
"We are equally concerned actually about the short periods of time over which that ballot will be conducted, a mere three days, which is very unusual. So we're also looking into this," he said.
Aer Lingus has asked IALPA to give a 15-day notice period before possible strike action, although the minimum legal requirement is 7 days.
The airline says it is seeking to reduce disruption for customers, although IALPA argues that 15 days of notice would allow Aer Lingus to avoid paying compensation fees.
The threatened industrial action comes in response to a wage dispute, with negotiations stalling last Thursday between the union and Aer Lingus.
Pilots had been seeking a 23.8% pay increase, a motion viewed by many as reasonable given the effect of inflation on their pay packets.
IALPA also highlighted the bumper profits made by Aer Lingus in 2019, arguing that this should trickle down to workers.
The airline recorded an operating profit of €225 million for the full year 2023, an increase of €168 million on 2022.
Aer Lingus has, however, branded a 23.8% pay rise "unsustainable".
Last week, IALPA rejected a Labour Court recommendation that pilots accept a 9.25% lift.
