More than 1,000 Thomas Cook cabin crew are being balloted on possible strike action which could cause major disruption during the May half-term holidays.
Unite says changes to rest breaks could see cabin crew only being allowed a 20-minute break during an 11 hour 59 minute shift.
Before the change, crew could expect a 20-minute break every six hours.
The ballot comes as Unite said it has concerns that cabin crew are being “pushed to the limit in a bid to maximised profits”.
The union says this is putting passenger safety at risk.
A member of the cabin crew will usually work a 10-15 hour shift which includes in-flight preparation, safety and security checks, boarding, inflight service of headsets, drinks, food, duty free sales and other promotions.
On short-haul flights this process can take place with just an hour turnaround, the union has said.
It says new services introduced by Thomas Cook on top of this - such as passengers being able to pre-order their duty free online and have it delivered to their seats - is adding to cabin crew’s workload.
The ballot closed on 25 May and the union has admitted it could disrupt the forthcoming half term school holidays.
A spokesman for Unite told The Independent that they could not make any decisions about when the strike might be until the ballot was completed.
Unite national officer Oliver Richardson said: “Our members are deeply concerned about the impact these changes to rest breaks are having on inflight safety. Fatigue is a major contributory factor to accidents and slower response times when there is an incident.
“The primary purpose of cabin crew is the safety of passengers, but instead Thomas Cook seems intent on working them to the bone to extract as much money as possible out of passengers at the expense of safety”.
He accused the airline of refusing to agree to talks to reach a “sensible negotiated solution”, saying it was “only inflaming matters”.
He said: “Thomas Cook needs to drop its high handed approach, listen to cabin crew and start to negotiate meaningfully with Unite. Otherwise, its work until you drop, no matter what the cost, ethos will harm passenger safety and customer service.”
A spokesman for Thomas Cook said: “We would like to reassure our customers that nothing matters more to us than safety. It’s regrettable the union has chosen this path because the crew rest procedure, which includes monitoring all crew rest on all flights, was introduced with the agreement of the union.
“It also meets the regulations of industry experts the Civil Aviation Authority and does not compromise on safety. We have offered to meet union representatives and the message we hear directly from our crew is that they’re looking forward to a great summer of flying customers on holiday.”
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies