(CNN) - British Airways pilots will strike in September for three days over a pay dispute, the first pilot walkout in about four decades.
Their union, the British Airline Pilots Association, on Friday announced the three dates — September 9, 10 and 27 — adding that it had proposed several packages to British Airways that had been rejected.
Last month, pilots voted 93% in favor of striking.
It will be the first time BA pilots have gone on strike since the 1970s. "They do so as a last resort and with enormous frustration at the way the business is now being run," the union said in a statement. It named issues like pay cuts and the loss of annual leave days.
The union estimated that the three days of strikes would cost the airline about £120 million, or roughly $147 million. The difference between BA's and union's proposals would cost the airline only about £5 million, or $6 million, the union claimed.
British Airways called its pay offer of an 11.5% increase over three years "fair" and above the United Kingdom's current rate of inflation. In a statement, it said the strike could "destroy the travel plans of tens of thousands of our customers." It called the strike "a reckless course of action."
It said it would adjust its schedule but that it still remained likely that many customers would need refunds or to rebook travel due to canceled flights. It said it was also considering using aircraft and crew from other airlines, as well as scheduling larger aircraft from partner airlines to fly the maximum number of customers.
CNN Business' Jill Disis contributed to this report.
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