Lufthansa Technik Airmotive Ireland has confirmed the company is to close its jet engine overhaul facility in Rathcoole, Co Dublin.
The company served notice of termination of employment on all 411 staff at the plant today.
LTAI announced the start of a 30-day process to consider closing the company in November, subject to consultation with all relevant parties.
The company said an offer from an outside party to take over the facility did not lead to any acceptable offer.
It also said negotiations with the three trade unions and employee representatives failed to identify any viable alternatives or to reach agreement on severance terms.
Talks between unions and representatives of Lufthansa management took place at the Labour Court today.
The Labour Court has recommended that the unions accept the severance deal on offer from the company.
This deal involves workers receiving statutory redundancy, plus four weeks per year of service.
The unions had been looking for six weeks per year of service.
The Labour Court hearing was originally scheduled for 9 January, but was brought forward to today.
Staff at the plant were told last month that it would close in the New Year.
Since then, unions and management have been involved in a 30-day consultation period that unions had hoped would result in a compromise that would save at least some of the jobs.
Originally, 20% of staff were due to leave the company by the end of January, 60% by the end of February, a further 10% to depart by the end of March and the balance would leave at the end of June.
However, sources said it was likely that the closure would take place over a faster time scale.