London, England (CNN) -- British Airways is offering to let customers rebook flights at no charge if they are affected by a cabin crew strike announced this week, but the airline is not offering refunds unless flights are actually scrapped, it said Tuesday.
The airline also announced Tuesday it is going to court to try to prevent the strike over the busy holiday period by Unite, the union representing flight crews.
"British Airways is commencing legal action in an attempt to protect customers from the massive stress and disruption threatened by Unite's decision to call a 12-day strike from December 22," the airline said in a statement. It claims there were "flaws" in the union's vote to strike.
The airline's competitors pounced on news of the strike, with Virgin Atlantic announcing it would fly larger planes on routes between London and New York, Newark, Boston, Washington and Delhi. It estimated that it would make about 1,600 extra seats available during the walkout.
BA rival airline BMI immediately took out newspaper ads in response to the strike, including one reading, "BA, humbug."
More than 12,500 BA employees, asked by Unite to cast ballots in November, voted by a 92.5 percent majority to walk out from December 22 for 12 days, Unite Deputy General Secretary Len McCluskey announced Monday.
The strike vote came after the airline introduced cost-cutting measures including a two-year pay freeze and reducing the numbers of cabin crew members on long-haul flights.
BA says the changes, introduced in the wake of a record pre-tax loss of more than $485 million for the six months from April to September, will save the airline $665 million.
McCluskey warned that the strike would inflict "catastrophic damage" to the airline if it went ahead and urged British Airways bosses to return to the negotiating table. He said union members had been pushed into a corner by BA Chief Executive Willie Walsh.
"We've been saying to Mr. Walsh this seems crazy at a time when British Airways is suffering badly through an economic downturn that he should force us into a dispute that would have catastrophic effects on the economy of the company," McCluskey told CNN Monday.
"That's why we're hoping that even at this late hour the strength of feeling of our members will get through to the company. We are available 24 hours a day to meet the company. If they are up for getting an agreement, I'm confident we can get one."
McCluskey said passengers, upset at having their holiday plans disrupted, should take their anger out on the airline. McCluskey said his members were not "mindless militants" but decent men and women who had been forced into a corner by British Airways.
But Walsh said a strike was "completely unjustified" and called on union chiefs to resume negotiations. He said the airline had agreed to pay cuts with pilots and more efficient ways of working with engineers, while a third of managers had taken buyouts.
BA cut 1,900 jobs over the summer through reduced overtime, increased part-time work, and voluntary buyouts. But it plans to eliminate 3,000 more jobs by March 2010, Walsh said last month.
CNN financial correspondent Richard Quest said the impact of the potential strike would be devastating for BA and said the consequences would be disruption for BA passengers and higher prices for travelers booking on other airlines.
"Their planes are (crowded) and they are now about to face a strike," Quest said. "They are going to have tens of thousands of passengers who are concerned, who are worried. I imagine anyone who is going away for Christmas is now thinking about shifting their booking if they can."
A representative of the Association of British Travel Agents, which represents travel agencies and tour operators in the United Kingdom, said passengers booked onto BA flights should wait and see what contingency plans the airline puts in place and whether the strike goes ahead.
"Hopefully the strike could be called off, and if you cancel your flight now then you may not be able to claim a refund," she said.
Unite has called on Britain's High Court to rule on whether BA's cutbacks have breached its member's contracts but the case is not scheduled to be heard until February 2010.
CNN's Ayesha Durgahee and Jim Boulden contributed to this report.