British Airways (BA) cabin crew members are planning 20 days of strikes in May and June, starting next week.
Members of union Unite will stage four separate strikes, each lasting five days.
The first strike will start next Tuesday (May 18) and end on May 22.
There will then be three further sets of walkouts, starting on May 24, May 30 and June 5.
It will be the third wave of strikes by Unite cabin crew, due to the ongoing quarrel over pay and working conditions.
A BA spokesperson said the decision has "no semblance of justification".
"Unite's officials continue to operate in their own world, showing callous disregard for our customers and their own members in all parts of our airline," said BA.
"We have made a very fair offer, which meets the concerns the union raised during 14 months of negotiations and also ensures that our crew remain the best rewarded in the UK airline industry. That offer remains available."
BA has already said it plans to operate all flights to and from Gatwick and London City airports.
A "substantial part" of longhaul flights from Heathrow will operate, said BA, as well as "a number of daily flights to every destination" in the airline's shorthaul network.
"We are confident that many crew will again ignore Unite's pointless strike call and support the efforts of the rest of the airline to keep our customers flying," said BA.
"We are speaking to a number of carriers about leasing in extra aircraft to support our shorthaul schedule and also obtaining thousands of seats from other airlines to help our customers rebook if their original flight is cancelled."
BA's revised Heathrow schedule will be announced a few days before the strike is due to start.
Unite's joint general secretaries Derek Simpson and Tony Woodley said cabin crew have been left with "no choice" but to strike.
"There can be no industrial peace without meaningful negotiations and while management victimises trade unionists and uses disciplinary procedures in a witch-hunt," said Simpson and Woodley.
"Passengers and investors alike will be dismayed that British Airways' management rejected an approach by the union over the weekend, after their offer had been comprehensively turned down by their own employees."
Unite balloted its cabin crew members on the latest offer from BA to end the dispute, which saw 81% reject the deal.
The union said it intends to hold a further industrial action ballot of BA cabin crew "over issues which have arisen from the company's conduct during the dispute".
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