British Airways cabin crew are starting a fresh wave of strikes today in a dispute over pay.
BA says long haul flights will fly as scheduled, however it is believed that some short-haul flights from Heathrow may be affected.
Intending passengers are advised to check the airline's website for any changes to flights.
Members of Unite will walk out for three days and will strike for a further three days from Thursday.
The workers are in BA's so-called mixed fleet, who have joined the airline since 2010.
They claim to be on "poverty pay", saying some are forced to take second jobs.
The strikers will mount picket lines near Heathrow Airport.
BA said all its passengers will be able to fly to their destinations despite the industrial action, with just a few short haul Heathrow flights having to be merged.
"This will mean some customers will travel slightly earlier or later in the day than originally booked. We are contacting those customers with the options available to them.
"Our pay offer for mixed fleet cabin crew is consistent with deals agreed with more than 90% of British Airways colleagues, including many Unite members.
"More than 9,000 cabin crew, represented by a different Unite branch, this week voted overwhelmingly to accept the deal.
"The offer also reflects pay awards given by other companies in the UK and will ensure that rewards for mixed fleet remain in line with those for cabin crew at our airline competitors," said a statement.
Unite national officer Oliver Richardson said: "Mixed fleet cabin crew members continue to show great courage in taking a stand against poverty pay at British Airways.
"Rather than issuing threats and wasting huge amounts of cash on chartering aircraft to cover striking cabin crew, British Airways should start valuing staff who contribute massively to the billions of pounds in profits the airline generates.
"British Airways needs to stop defending some of the lowest basic salaries in the airline industry and start addressing pay levels, which are forcing mixed fleet cabin crew into debt and second jobs to make ends meet."
Unite said basic pay for the cabin crew involved in the row starts at £12,192 with £3-an-hour flying pay.
Unite estimates that on average mixed fleet cabin crew earn £16,000, including allowances, a year.
BA disputes the figure, saying no-one earns less than £21,000.