The first day of a 48-hour work stoppage by British Midlands cabin crew, check-in staff, ground staff and baggage handlers is now underway.
The union hit out at the company, saying it was playing hard ball in the planned transfer of ground operations out of Dublin.
Union representative Ben Carney said staff were angry at the way they have been treated.
"Nobody wants a strike but sometimes they are inevitable. Our staff are very sore about the sell-off without any notification. They were left in the lurch and feel hard done by," he said.