Leeds-based airline Jet2 has confirmed it is planning to cut jobs and its flight schedule.
Union leaders say 102 pilot jobs are to go. There are reports that as many as 380 cabin crew staff will lose their posts.
The airline would not confirm job numbers. But did say redundancies are proposed across the business.
Jet2 is not due to resume flying until July 15, which means that its entire fleet will have been grounded for more than three months.
Brian Strutton, the general secretary if the pilot's union Balpa, said: "Many of the pilots whose jobs are on the line in Jet2 have just recently moved there after having lost their jobs at Thomas Cook.
"These pilots have been through the mill already."
He added: "Despite being one of our least union-friendly airlines, I hope Jet2 negotiates in good faith and works with us on how we can mitigate these proposed losses and see Jet2 thrive in the future."
A Jet2 spokesperson said: "We have had to reassess and reduce our flying programme for the remainder of 2020 and for 2021. Sadly, the overall effect of these reductions has been the need to propose a number of colleague redundancies across our business.
"We cannot say how much we regret these proposed redundancies and we will be consulting with appropriate representatives of the affected colleagues in order to ensure that all options and issues are fully considered."
Jet2 is the latest airline to begin consulting on redundancies as the aviation industry struggles to cope with the collapse in demand caused by the coronavirus pandemic.
Other carriers that have announced job cuts include British Airways, easyJet and Ryanair.