British Airways is taking legal action to halt a 12-day strike planned by cabin crew over Christmas, alleging balloting irregularities.

The airline called on (union) Unite to call off the industrial action by 1400 GMT. The union has not done so and BA is now seeking an injunction to prevent the strike going ahead, the flag carrier's chief executive Willie Walsh said in a statement on Tuesday.

BA cabin crew voted on Monday to walk out from December 22, escalating a dispute over job losses and changes to working practices.

The airline said it had written to Unite, highlighting irregularities it believes render the ballot invalid.

BA believes ballot papers were sent to staff who had left the company or were in the process of leaving and should not have been balloted, breaching industrial relations law, a BA spokeswoman said.

Some 13,000 BA staff were balloted by Unite, 92.5 percent of whom favored industrial action.

The airline wants three quarters of its crew to accept pay rises of between 2 and 7 percent this year and a pay freeze in 2010, and for 3,000 staff to switch to part-time working, along with a reduction in onboard crewing levels from 15 to 14 on long-haul flights from London's Heathrow airport. Shares in BA fell 2 percent to 197 pence by 1550 GMT (10:50 a.m. EST) after analysts said the strike could result in the airline losing upwards of 250 million pounds ($406 million) in revenues.

Although BA is still to announce the contingency measures it will take, we estimate that the cost of the strike over the 12 day period (pre-depreciation) could (be) 40 to 50 million pounds in lost profits and 250 to 275 million in lost revenues, said UBS analyst Jarrod Castle.

Astaire analyst Douglas McNeill said a deal to avert the strike was unlikely and that BA management had showed no inclination to back down because it would have to unpick deals it had made with other sections of its workforce.

Richard Branson, founder of BA rival Virgin Atlantic, called on the British government to step in to prevent damage to passengers' holiday travel plans in future.

It's obviously extremely damaging to everybody, the company, employees, and most importantly the traveling public, Branson told Reuters.

In this day and age there must be a better way than strikes to resolve differences -- maybe government should try to look at other ways to resolve disputes rather than the old fashioned way that will mess up so many people's lives.

(Editing by Paul Sandle, John Stonestreet)