Cityjet has told unions representing staff at the airline that it is to begin a consultation process on redundancies that could lead to up to 276 employees across its Irish and UK operations leaving the organisation.
It is expected that the redundancies will impact the airline's administration, flying and engineering support staff.
A further 400 staff in its operations in various cities across Europe also look likely to lose their jobs.
The company said the move is a response to the need to reduce its size, because of the impact on its business from Covid-19.
"CityJet has operated from Dublin for almost 27 years so this is a sad time for us as we must react to market conditions and enter into an enforced downsizing of our core infrastructure," said Pat Byrne, Executive Chairman of CityJet DAC.
"CityJet is made up of hundreds of dedicated people with extraordinary skills and it is sincerely regrettable that we now must prepare to lose the skills and services of so many of our loyal and excellent colleagues."
Last month Kieran Wallace of KPMG was appointed examiner to Cityjet DAC by the High Court.
According to the company a full review is now being conducted of the business with a view to restructuring it in such a way that it can be made sustainable for the future.
"This includes the current shape and size of the company, the current and potential business opportunities and the cost base and structures required to deliver a successful future," the company said in a statement.
Prior to the crisis, Cityjet had been flying its aircraft on routes on behalf of other airlines, such as SAS and Aer Lingus, through a service known as wet leasing.
It employed 1,175 people, more than 400 of whom are based in Dublin where its headquarters is located.
"Although all capacity had been placed for 2020, the Covid-19 crisis saw four of the airline's five planned customer airlines cancel their contracts in March, leading to a significant reduction in the scale of the planned operation," the airline said.
The company said a number of the contracts for European airlines were supported out of Dublin.
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It has also decided to remove the Avro RJ85 from its fleet because of the contract terminations, a move which will impact some pilots who are only qualified to fly these aircraft.
CityJet is also closing the majority of its European bases in locations such as Helsinki, Stockholm, Paris, Vilnius, Tallin and Brussels.
Talks are ongoing between management and staff in these locations, with up to 400 redundancies expected.
However, its Copenhagen base is remaining open in order to continue to service a contract with SAS.
The High Court was told last month that the company has debts of €500m and currently has a net deficit of liabilities over assets on a going concern basis of €186m.
It operates a fleet of 34 aircraft, including 28 CRJ900 jets and eight Avro RJ85s.