Aer Lingus has warned it will start suspending pilots who refuse to help in the recruitment of crew for the airline's Belfast operation from tomorrow.
Meanwhile Siptu said it would consult with other unions at the airline with a view to taking industrial action over the imposition of a pay freeze pending the implementation of a €20 million cost-cutting plan.
The pilots today received a letter from Aer Lingus chief executive Dermot Mannion threatening suspension with immediate effect if they refuse to carry out duties which, management contend, include assisting in recruitment and training.
The carrier wants its pilots to participate in the recruitment and training of new staff operating out of Belfast. But the pilots are objecting because the new staff will receive inferior pay, terms and conditions compared to existing staff.
Impact, which represents the pilots said the threat was counterproductive and would not change its position on non-co-operation in the short term.
In short statement issued this evening the company said some of the members of its pilots' executive council were on duty and that a response would be considered at a meeting tomorrow.
"Impact believes that the threat of suspension, issued during an ongoing period of intense negotiations, is counterproductive to both the company's objectives and the ongoing negotiations," the statement said.
The letter is the latest controversial step taken by management implementing a restructuring plan at the company, which it says is needed urgently to keep the company competitive.
The decision to move its Heathrow slots from its Shannon route to Belfast has caused widespread outrage and a political headache for the Government.
Siptu officials met Aer Lingus management today and afterwards said it had told the company its decision to impose the pay freeze, which affects 3,600 workers, breached the social partnership agreement Towards 2016.
Siptu national industrial secretary Michael Halpenny said the company was also in breach of commitments given last February not to allow the opening of new bases to lead to job losses elsewhere in the company.
The fight to save jobs and connectivity for Shannon was not over, Mr Halpenny added.