A vote for industrial action would clear the way for a third wave of strikes The result of the latest strike ballot of BA cabin crew is to be announced, on the same day as the company completes its merger with Spanish carrier Iberia.
Members of the Unite union are expected to vote for more industrial action in its long-running dispute with bosses.
The dispute is over several issues, including the restoration of previous strikers' travel concessions.
The merger will create a new holding company and shares will be listed on stock markets on Monday.
The Unite dispute, originally over job cuts, started nearly two years ago and has already cost BA £150m and led to 22 days of strikes.
Unite's new leader Len McCluskey said he hoped BA would take note of the ballot result and try again to resolve the dispute.
Speaking after a mass meeting of more than 1,000 cabin crew last week, he said: "If the company believes they have broken the spirit of the cabin crew, they should have been at this meeting to witness the anger of people."
The union will have to give seven days' notice of any strikes.
BA has said it has contingency plans and in the event of another strike, it would be able to run normal timetables from London Gatwick and City airports, and all long-haul and many short-haul flights from Heathrow.
BBC employment correspondent Martin Shankleman said the start of a new era for BA could be marred by the return of strikes.
"Union sources are predicting another vote for action, clearing the way for a third wave of strikes probably this spring," he said.
In addition to the restoration of travel concessions, Unite is also calling for an outside review of all disciplinary cases against members.
Meanwhile, the completion of the merger is expected on Friday and shares in the new holding company, International Consolidated Airlines Group (IAG), will be listed on stock markets in London and Madrid on Monday.
It comes nearly 24 years after BA joined the London Stock Exchange in a high-profile flotation that was 11-times oversubscribed.
BA and Iberia will retain their brands as part of the move that is expected to save 400m euro (£337m) a year by its fifth year.
The new airline group will have 419 aircraft flying to 205 destinations and will be Europe's second biggest airline by market value after Lufthansa.
Willie Walsh will step down as chief executive of BA to take up the same role at IAG in a move that will see his basic pay increase 12% from £735,000 to £825,000 a year.
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