Irish-based Ryanair pilots are expected to announce strike action later today.
Some 170 pilots have been balloted for industrial action with the result due to be announced in the coming hours.
Their UK-based colleagues have already announced a total of five strike days at the end of this month and the start of September.
It could result in thousands of people having their flights cancelled; however, the airline has insisted it will do its utmost to avoid disruption.
Aviation Journalist Gerry Byrne believes Irish pilots will vote to down tools in their dispute over pay.
“All the indications are that there will be support for strike action,” he said. “It seems to be the trend.”
“The UK pilots recently voted for strike action and there have been other pieces of industrial action.
“There appears to be dissatisfaction among pilots – no Ryanair of course will disagree strongly with this – that Ryanair is not playing ball, as it were.”
The UK dispute centre on a range of issues including pensions, loss of license insurance, maternity benefits, allowances and pay.
Pilots have insisted they do not wish to disrupt anyone’s travel plans – and said they have no choice but to strike.
Mr Byrne said any strike among the Irish pilots would hit passengers badly.
“It would have a very dramatic effect,” he said. “It is, as you say, coming in to the tail end of the summer season August and September and the British pilots are going to strike around that time – they have a total of five days already earmarked.
“We are not told when the Irish pilots are likely to strike.”
Ryanair has urged UK pilots to return to talks and has apologised to customers.
The industrial disputes come just a week after Ryanair announced a 21% fall in profits and said up to 900 jobs were at risk.