The UK's Unite trade union has called on Thomson Airways to guarantee there will be no compulsory redundancies as the carrier looks to reduce cabin crew numbers by around 600.
Thomson, part of German travel giant TUI, has begun a 90-day period of consultation with staff over the potential job losses.
The cuts are driven by the airline's upgrade of its fleet. It will have taken delivery of 22 new 189-seat Boeing 737-800s by summer 2013, replacing its older, 233-seat 757s which require higher crew numbers.
Unite regional officer Kevin Hall said: "These cuts are a blow to the workforce during a time of economic uncertainty. Unite will be working constructively with the company and we are confident that we can substantially mitigate the impact of these cuts."
The carrier said it is "committed to mitigating the impact of these changes on cabin crew" and will work closely with the union to achieve this.
Meanwhile, parent company TUI saw turnover rise to €3.4 billion ($4.5 billion) in first quarter trading, for the period to 31 December 2011, from €3.2 billion a year earlier.
It said weaker demand in the UK had led it to redeploy aircraft from Thomson to Canada and the Nordics for the winter season. This reduced capacity enabled "satisfactory load factor despite lower customer numbers".
TUIfly Nordic took three additional aircraft for the period - two 737-800s (G-CDZH and G-CDZI) from Thomson and a further unidentified aicraft from French sister airline CorsairFly.
CorsairFly, meanwhile, was hit by declines in margins driven by "fierce competition" and erosion of earnings due to high fuel costs, TUI said.
TUI's Dutch charter airline, ArkeFly also added capacity for the winter season, taking on an additional aircraft, thought to be a Boeing 767-300ER (PH-OYE) formerly operated by Thomson.