AER Lingus today announced plans to make 676 job cuts as part of a bid to save almost 100 million euro (£92 million).
The Irish airline said it could not continue with its current operating costs and insisted the redundancies were essential to bring the firm into line with competitors.
Around 489 cuts are expected to be made from pilots, ground handling and cabin crew, with a further 187 redundancies from head office and support areas.
The job losses come as part of a wider proposal aimed at cutting operating costs by 97 million euro (£90 million) before the end of 2011.
As part of its Transformation Plan the airline is also set to introduce banded reductions in wages for staff whose basic pay is more than 35,000 euro (£32,000).
The trade union Impact, which represents 1,500 cabin crew at Aer Lingus, described the cost reduction plan as radical and severe.
"That the proposal also contains such a significant number of cabin crew job losses is, in our view, deeply unfair and devastating to our members," a spokesman said.
But Aer Lingus, which currently employs 3,879 staff, said it could not continue operating with an uncompetitive cost base compared to its rivals.
The airline’s chief executive Christoph Mueller said he regretted the impact the cuts would have on employees.
"However, we must transform the business now to ensure that Aer Lingus has a business model for the long-term and can deliver value for all stakeholders," he added.
The airline said while it hopes many of the redundancies will be voluntary, compulsory redundancies may prove necessary.
The first set of 489 cuts is expected to be completed next year, with the 187 redundancies from head office and support areas completed by 2011.
A six-week consultation process is now under way between the airline, employees and union representatives, with discussions expected to conclude by November 18.