British Airways cabin crew are set to launch the last wave of five-day strikes in their bitter row with the airline, although further industrial action is threatened unless the deadlocked row is broken.
Members of Unite will stage their 18th day of action since March and will stay out until next Wednesday, forcing more losses onto the company.
The union said the strikes had cost BA £119 million, with the airline admitting each day of action was adding £7 million.
The impact of the dispute was revealed when the airline announced a 14.2% dip in passenger numbers last month. BA said it plans to increase its flying programme over the next five days as more crew "ignore" the industrial action and report for duty.
"We have announced that we are planning to fly about 80% of our long-haul programme, including all JFK (New York) services and also all South African flights as we approach the World Cup," said a spokesman.
Unite is planning to hold another ballot of its cabin crew members, which it has to under employment law, and has warned of a summer of disruption unless there is a deal. Talks between Unite's joint leader Tony Woodley and BA's chief executive Willie Walsh under the auspices of the conciliation service Acas ended without agreement last week, with little sign of any progress.
An agreement in principle has been struck over cost-cutting, the original cause of the dispute, but the removal of travel concessions from strikers is now blocking a deal. Unite has urged BA to fully restore the travel concessions, arguing it would not cost the airline any money.
The union said it believed the next series of strikes will be strongly supported by cabin crew and will have a "huge impact" on flights.
Singer Billy Bragg will perform an impromptu gig for the strikers at a football ground near Heathrow.
Unite will increase strike pay, currently £30 a day, for the next five-day walkout, in recognition of the financial hardship the workers are facing.