Members of British Airways mixed fleet cabin crew are to stage a two-week walkout from 1 July over pay and travel concessions, according to Unite union.
There had been a four-day strike planned from today, but that had been suspended for new talks to take place at conciliation service Acas.
The union said the airline would not accept its "final compromise position" regarding a row over the sanctioning of striking cabin crew, saying benefits have not been reinstated for them.
Unite assistant general secretary Howard Beckett said: “The refusal by British Airways bosses to meaningfully consider our compromise offer is deeply disappointing.
“A resolution to this long-running dispute was within the grasp of British Airways, but instead of grabbing that opportunity, bosses rebuffed it. It now means British Airways faces an entirely avoidable two week strike and prolonged legal action on behalf of over 1,400 mixed cabin crew."
Unite believes the divisive way British Airways has targeted striking members of cabin crew is unlawful. The airline should be under no illusion of Unite's intent to pursue justice on behalf of its members all the way to the highest court in the land.
BA said in a statement:
As for previous periods when Unite called strikes of mixed fleet cabin crew, we will fly all our customers to their destinations.
This proposed strike action is extreme and completely unnecessary. We had reached a deal on pay, which Unite agreed was acceptable. Unite has already confirmed it is pursuing the non-pay issues in this dispute through the courts.
We urge Unite to let its members vote on the pay proposals.
The airline said it will publish contingency plans in "the coming days" to provide guidance for customers who have bookings on the days of the threatened industrial action.
Read more: BA cabin crew launch fresh round of strikes
To date, there have been 26 days of strike action since the beginning of January in the long-running row over pay.
Unite had said the mixed fleet cabin crew, who work both short and long-haul routes, are paid less than other BA crew.
The union then said 1,400 of its members had their travel benefits taken away as a result of the industrial action, the cause of the walkout which had been due to start today.
BA had called the four-day strike lined up "completely unnecessary", saying it had reached a deal on pay "which Unite's national officers agreed was acceptable".
The fresh strike threat is another headache for the carrier which has been dealing with the fallout from a huge IT meltdown over the late May bank holiday weekend, causing mass flight cancellation across Heathrow and Gatwick airports and disrupting 75,000 passengers.
The chief executive of BA's parent company IAG, Willie Walsh, said at the firm's annual general meeting yesterday that the company's initial estimates posted the cost from the trouble at £80m.
The two-week strike dates:
From 00:00 Saturday 1 July to 23:59 Sunday 16 July