Monarch workers were charged up to £40 to call a premium rate phone line to be told they had been fired.
See also: Monarch collapse: What should I do now?
Pilots and cabin crew unable to make meetings where bosses broke the news of the airline's collapse on Monday had to ring an 0844 number for a conference call, at 40p a minute.
One pilot was charged £38.90 for the 1hr 15mins session, ordered by the stricken firm's joint administrators.
General secretary for pilots union Balpa, Brian Strutton called it a 'kick in the teeth' for the pilots and crew who were already down
Brian Strutton, general secretary of pilots' union Balpa, said: "This is unbelievably
cold-hearted. I am shocked to learn this was a premium rate call and pilots and other staff have been charged £40 for the privilege of being told they are out of a job. A kick in the teeth when they are already down.
"I'm asking administrators KPMG to rectify this. I think an apology is also in order."
Unite union national officer Oliver Richardson added: "It is outrageous that people losing their job should have to phone a national rate number and pay for the privilege of getting key information." The joint administrators said: "One of our priorities was to ensure all staff were communicated with as quickly and openly as possible.
One pilot was charged £38 during their hour-long conference call
Administrators for Monarch have insisted that the employees will be refunded any additional costs they incurred
"Having asked a third-party provider to set up a conference call for employees, and agreeing to pay for that facility, we have since been made aware the participants were charged an additional sum by their phone company to join the call.
"We will ensure all participants are refunded any additional costs they incurred."
The charges came as the biggest peacetime repatriation of 110,000 stranded Monarch passengers got underway.
But 2,000 staff were also affected. Unite, which represents 1,800 cabin crew and engineers, launched a legal action over failure to consult on the redundancies. Firms with more than 100 staff must give a minimum 45 days' notice of their intention to axe workers.