Britain's biggest union Unite said its members planned to strike for 12 days between December 22 and January 2 ? a decision BA chief executive Willie Walsh described as "senseless", while also vowing to stand firm over job cuts.

The industrial action comes at a critical point for loss-making British Airways, which is slashing costs and attempting to merge with Spanish carrier Iberia in a desperate fight to stay competitive.

"After long discussions... we are planning to withdraw our labour for a period of 12 days starting 22nd December," Unite said in a statement after staff voted 9-1 in favour of striking.

The announcement is a major blow for BA's many passengers that are planning to fly worldwide with the British airline over the festive period. BA had carried 2.34 million passengers in November.

"British Airways is extremely disappointed that Unite is planning massive disruption for hundreds of thousands of our customers over the Christmas/New Year holiday period," the airline said in a statement.

Walsh said there was "no justification for threatening such extreme action," adding: "It is very sad that they are seeking to use the Christmas holiday plans and family reunions of hundreds of thousands of people to try to pursue their case."

The chief executive also insisted that BA "will not be reversing... changes to onboard crew numbers." BA had in October announced it was cutting 1700 cabin crew positions and introducing a two-year pay freeze on staff keeping their jobs.

A total of 10 288 cabin crew voted on the strike action, with 92.49 percent in favour of the proposal.

Unite said the decision to strike was not taken "lightly, especially during the financial strife that the company finds itself in".

Merger under threat?

BA last month revealed that net losses quadrupled to #217-million in the group's first half, or six months to September.

On Monday the airline said that its pension deficit had ballooned to #3.7-billion, a 76-percent increase compared to the level in 2006, causing the airline to seek a "recovery plan".

The huge shortfall risks scuppering BA's proposed tie-up with Iberia, which has the right to walk away should BA fail to resolve the problem.

The merger is seen by analysts as a move by BA to avoid being sidelined by rivals Air France-KLM and Lufthansa, as the economic downturn and the rise of low-cost airlines drives airline alliances and steep cost cutting.

A combination of BA and Iberia would create one of the world's biggest airlines, as the two groups grapple with huge losses amid falling demand for air travel.

If you're flying with British Airways over this period, your flight may well be cancelled or rescheduled. The airline says it is adjusting flight schedules, and that customers should ensure their contact details are correct, by updating the 'Manage my Booking' service on ba.com. You can also Click here for more info on changing your booking.

Ed's note: The strike action will not affect domestic and regional flights operated by the franchisee BA/Comair. Only international flights operated by British Airways (i.e. to London and beyond) will be affected.