The union representing British Airways PLC's (BAY.LN) cabin crew Friday announced strikes will take place later this month after the U.K. airline and union leaders failed to reach a last-minute deal on changes to working practices.

Unite, the union representing cabin crew, said its members will begin a three-day strike March 20 and a four-day strike beginning March 27. The decision to strike likely will deter passengers from flying with BA over the period and potentially in the longer term, while also adding to BA's troubles. The company in February reported a pretax loss in the three months to Dec. 31 of GBP50 million compared with a GBP122 million loss a year earlier.

The union said it had received a new proposal Thursday from BA but didn't feel able to recommend the offer to its members at this time, and warned that further strikes could take place after April 14 if the dispute wasn't resolved. It will ballot members on BA's new proposals ahead of its first strike.

However, BA said its offer had been invalidated by the announcement of strike dates and the proposal was no longer on the table.

BA said in a statement that its offer to cabin crew had been reasonable and fair and that it was disappointed by the decision to strike. "Unite's action has no shred of justification," it added.

Unite's proposals to save the airline money fell significantly short of the savings that BA wanted to make and would leave crew members between GBP1,000 and GBP2,700 a year worse off, the airline said.

The strike, which Unite said could cost BA at least GBP25 million a day, would be the first for Chief Executive Willie Walsh since he took the helm of the U.K. carrier in 2005 and the first by BA cabin crew since 1997.

Unite accused Walsh and other executives of disrupting negotiations. "Every time talks appeared to make progress, the chief executive or another senior manager has popped up making public statements designed to inflame the situation," said Unite Assistant General Secretary Len McCluskey. "This has led to the view that BA management's real agenda is destroying trade unionism among its employees."

British Airways isn't alone in facing strike action by disgruntled staff. The severe downturn in the industry caused by the recession has caused airlines to post billions of dollars in losses and prompted them to cut costs and jobs as they react to lower revenue. Airlines including Deutsche Lufthansa AG (LHA.XE), AMR Corp.'s (AMR) American Airlines and Aer Lingus Group PLC (EIL1.DB) currently face industrial action by employees battling planned changes.

But others have avoided strikes. For example, Scandinavian airline SAS AB (SAS.SK) Friday said it had reached a collective agreement with flight crew unions, which will save the loss-making airline around 500 million Swedish kronor ($70 million) a year. Finalizing the deal was one of the conditions for the Swedish, Danish and Norwegian governments to participate in the carrier's proposed SEK5 billion rights issue, which was announced last month. The three countries jointly own 50% of the airline, which hasn't had a profitable year since 2007.

Walsh has long held his position that permanent change is needed at BA and has prepared a range of measures to combat industrial action.

BA last week said it has 23 leased aircraft on standby to cover services that could be hit by disruptions. It will lease planes complete with crew and pilots. It wouldn't say which routes they would cover.

Some 6,000 staff had volunteered to help in various areas, such as handing out advice at airports. That includes 1,000 workers who have volunteered to replace cabin crew during strikes. The airline has already been training pilots and ground staff as cabin crew.

"Should a strike take place, we will do everything we can to protect our customers' travel plans as far as possible," BA said. It plans to operate all its scheduled flights from London City Airport, all long-haul services and about 50% of short-haul services from Gatwick, and "a substantial part" of its long-haul and short-haul schedule from Heathrow.

BA said also that it was in the process of obtaining seats on flights operated by other carriers to enable thousands of its customers to fly to their chosen destinations.

Rivals were quick to step in. British Midland International, or bmi, a unit of Lufthansa, said it would do what it could to assist BA customers caught up in the dispute and currently was reviewing the possibility of flying larger aircraft and additional frequencies. Bmi is the second-largest operator at Heathrow after BA.

BA and unions have been battling for 12 months over how to save the airline money. After failing to come to an agreement, BA Nov. 16 took the step of reducing cabin crew on long-haul flights from London's Heathrow Airport to 14 personnel from 15 without union support. Last month, the High Court ruled that those changes weren't a breach of contract, meaning BA won't be forced to reverse the changes or to pay damages to staff.

This is the second time cabin crew have attempted to take industrial action after BA in December won an injunction to prevent a 12-day strike. BA won the injunction based on the grounds the union had balloted staff that weren't entitled to vote because they would have left the U.K. carrier at the time strikes were due to take place.

At 1336 GMT, BA's shares traded up 4 pence, or 1.9%, at 235 pence while the benchmark FTSE 100 index traded up 0.5%.

-By Kaveri Niththyananthan, Dow Jones Newswires; 4420 7842 9299; kaveri.niththyananthan@dowjones.com