British Airways cabin crew will strike on Christmas Day and Boxing Day in a row over pay, the airline has announced.
The airline said it was "appalled" at the decision by the Unite union and pledged to ensure its customers get to their destination.
The row involves around 4,500 so-called mixed fleet cabin crew who joined BA since 2010.
Unite say they are on lower pay than other staff.
BA, which employs around 16,000 cabin crew, said in a statement: "We have been informed tonight by Unite that it has called strike action by mixed fleet cabin crew on Christmas Day and Boxing Day.
"We are appalled that Unite proposes to disrupt customers' travel plans on such special days when so many families are trying to gather together or set off on well-deserved holidays.
"This calculated and heartless action is completely unnecessary and we are determined that it will fail.
"We will plan to ensure all our customers travel to their destinations so that their Christmas arrangements are not ruined. We will publish more details within the next 72 hours.
"Meanwhile, we have also approached the conciliation service Acas to seek their assistance in reaching an outcome that would avoid any possibility of disruption."
British Airways said the following routes would not be affected:
- All flights to and from London Gatwick
- All flights to and from London City
- All flights to and from Stansted
- Flights operated by subsidiary OpenSkies between Paris and New York
- Flights operated by British Airways franchise partners (Comair in South Africa and SUN-AIR in Scandinavia)
- Flights operated by other carriers (including oneworld Alliance partners) which have a BA codeshare flight number
The airline said it was aiming to operate all long haul flights to and from London Heathrow as normal, while some short haul flights from the airport would be affected.