Cabin crew employed under British Airways' mixed-fleet contract are planning to renew strike action unless the airline "hammers out" a new agreement on pay and conditions.
Trade union Unite says an ongoing strike by its members that had been due to end on 15 August will now be extended until 30 August.
Unite is protesting against what it calls "poverty pay" for its members and has grievances relating to working conditions. It describes as "half-hearted" an offer by BA to reinstate travel concessions for workers who took strike action.
The airline says: "More than three months ago Unite agreed that our pay deal was acceptable but have since refused to ballot their members on it.
"Last week we took the significant step of offering to return staff travel to crew who had been on strike, which was the biggest outstanding issue in the dispute, in order to bring the dispute to an end. Unite has now chosen to reject this offer and call yet more strikes."
The IAG-owned carrier is currently using aircraft wet-leased from Qatar Airways to operate short-haul flights and says it will "ensure our customers reach their destinations".
BA seeks to rebut the union's complaint that bonuses have been removed from striking staff. The airline says: "We confirmed back in April that they would be eligible for the 2017 bonus."