Aer Lingus has no long-term commitment to the Midwest and may pull out of the region, unions said today.
A union umbrella organisation, the Shannon Action Group (SAG), claimed the airline may withdraw or run down services further next year.
Aer Lingus has already decided to cease its service between Shannon airport and Heathrow and set up a base in Belfast.
"Staff members have heard members of the management executive team discussing the need to pull out of Shannon as quickly as possible," Siptu's Geraldine Morrissey, who is also a member of SAG, said.
"They made the comments on board an aircraft when, presumably, they thought they were out of earshot," she added.
"We had commitments through the Labour Court process that no jobs would be lost as the result of Aer Lingus opening new bases, yet this is precisely what has happened in Shannon with the reallocation of Heathrow slots to Belfast.
"The open skies agreement provides an opportunity to pull out completely, and Aer Lingus management makes no secret of the fact that it does not want to be here in the first place."
The SAG is part of the Atlantic Connectivity Alliance and will be participating in a picket of Leinster House on Wednesday morning. The Dáil is due to debate a Government motion on the Aer Lingus decision that afternoon.
