British Airways cabin crew launched a two-week strike on Saturday as part of a long-running pay dispute with the airline.
The "Mixed Fleet" crew, who work on long- and short-haul flights and are based at London's Heathrow airport, are set to stay off the job until July 16.
The strike comes after a recent breakdown in pay talks between the company and union representatives.
The Unite union has said employees in the "Mixed Fleet" category, which was created by British Airways in 2010, receive lower pay and less generous terms than other crew members.
British Airways has said the pay is in line with its competitors.
"Customers will take a dim view and a great British brand risks being further tarnished. We call on British Airways to drop the threats and drop the sanctions and resolve this long-running dispute," Unite national officer Oliver Richardson said in a statement.
British Airways warned of further consequences for those who went on strike, but said all customers would reach their destinations.
Solicitors Bott & Co said around 400,000 passengers could be affected over the 16-day strike period.
Willie Walsh, CEO of BA's parent company IAG, said on Thursday that he expected all passengers to fly, as BA had applied to use 9 Qatar Airways planes, with staff. That application was approved on Friday
While Britain's busiest airport, London's Heathrow, will be hit by the walk-off, other airports in the capital will not be affected.
The mixed fleet crew first threatened to strike over Christmas of 2016. Although that was called off, there have been 26 days of strike action so far this year.
The mixed fleet staff make up about a third of the BA's total cabin crew of around 16,000, although not all members of the crew will take action.
Unite said that 1,400 mixed fleet members who had been on strike previously had seen bonus payments and travel concessions removed.
"We have set out the consequences for crew if they take strike action," British Airways said in a statement.
"The purposes of these consequences are to encourage crew to come to work."
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