Unite, the union representing British Airways’ cabin crew, scheduled a walkout after the two sides failed to reach a labor deal this week.
Strikes are planned for March 20 to 22 and March 27 to 30. The union said it stuck to a promise not to strike during the Easter holiday.
Unite said it will hold a "consultative ballot" with union members on March 19 to consider an offer submitted by British Airways on Thursday, but Unite is not recommending that the cabin crew accept it.
The dispute between the airline and its cabin crew has grown acrimonious. Earlier this month, British Airways CEO Willie Walsh said there are 6,000 volunteers ready to step in should the cabin crew walk out, and that nearly 1,000 of the volunteers have been trained.
Len McCluskey, Unite's assistant general secretary, accused Walsh of adopting an "inflammatory and confrontational stance at a time when we are engaged in meaningful talks with the company."
British Airways has about 13,500 cabin crew.
In the event of a strike, British Airways earlier this month said it would operate all flights from London City (including recently launched service to New York), all long-haul flights from London Gatwick and about half of its short-haul flights from Gatwick.
At London Heathrow, the airline said it would operate "a substantial proportion" of long-haul flights and "a good number of short-haul flights," assisted by chartered aircraft with crews from other airlines in the U.K. and Europe.
"We have also arranged to secure seats from other carriers, so thousands more of you can reach your chosen destinations," Walsh said.