Unite has ratcheted up its bitter dispute with BA by deciding to go to court over the withdrawal of travel perks from the airline's striking cabin crew.
The carrier withheld the concessions whereby staff travel on reduced fares after a series of strikes disrupted its operations earlier this year.
The union which represents the bulk of the striking cabin crew said the withdrawal breaches European human rights laws.
In a statement it said it also believed "this sanction - which has impeded the resolution of the long-running dispute - was taken without proper disciplinary procedures being followed."
The withdrawal of travel perks ands the airline's subsequent refusal to re-instate them for striking staff is one of the last stumbling blocks to a settlement in the long running dispute.
The row originally started over changes to working practices among cabin crew imposed by the airline.
The latest ballot among cabin crew has given Unite a further mandate to call more stoppages.
But the union said it would be meeting BA officials at ACAS, the UK arbitration service, next week.
It is also planning to meet cabin crew representatives to review the current situation.
Cabin crews have walked out for a total of 22 days this year which is estimated to have cost the loss-making airline £150m.
Derek Simpson and Tony Woodley, the union's joint general secretaries, said: "Unite remains determined to secure a settlement to this dispute acceptable to cabin crew.
"Until such an agreement is secured, we will continue to support our members financially and legally to ensure that every avenue is explored to achieve justice for these loyal and professional men and women who have been so badly treated by their employer."
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