Thousands of air passengers are at risk of having no flights as Aer Lingus management and unions return to the Labour Relations Commission.
This second day of talks will attempt to bring an end to the ongoing pilots dispute.
Seven pilots remain suspended without pay and the airline says any others who refuse to train new recruits for its Belfast hub will also be suspended.
"We'll give whatever it takes and we're here for as long it takes, and we want to reach a solution for this - we want to reach an agreement with Aer Lingus on the outstanding issues relating to the Belfast base," said IMPACT's Michael Landers before he went into the meetings.
"We're certainly coming here just for show or for form or anything like that," he said.