British Airways staff will stage a two week strike in August.
Members of the airline's 'mixed fleet crew' - working on both long and short haul flights - will walk out for 14 days from August 2 over pay.
Crew members have already taken 46 days of strike action in what is becoming one of the longest-running disputes in the aviation industry.
The new action by members of the Unite union means the cabin crew will have been on strike for four weeks.
Unite claimed cabin crew who are covering for striking workers would be getting "perilously close" to their legal number of flying hours.
National officer Oliver Richardson said: "Attempts by British Airways to bribe cabin crew into not striking with a £250 bung represent a crude attempt to sow division and will ultimately fail.
"Rather than spending money on crude bribes and millions on 'wet' leasing aircraft to defend its low pay and bullying behaviour, it's time British Airways started talking about resolving this dispute, which will further tarnish its brand."
Unite has launched legal action against the Government's decision to give the go-ahead to the "wet lease" of nine Airbus aircraft from Qatar Airways during the strike.