London, England (CNN) -- British Airways cabin crew members went on strike Saturday, leaving thousands of would-be passengers' travel plans during the next two weeks in disarray.
The strike came after British Airways Chief Executive Willie Walsh and the joint general secretary of the Unite union, Tony Woodley, emerged Friday from a meeting and announced the effort to avert the walkout had failed.
"This company does not want to negotiate," Woodley said of British Airways. "This company wants ultimately to go to war with my members and the union."
Walsh said he "deeply regrets" the inconvenience the strikes will cause to passengers but said the company will still try to operate as many flights as possible. "I am disappointed the union has not been able to see the sense of the proposal we tabled today," Walsh said.
British Airways posted lists on its Web site of flights that it plans to operate during the walkout.
A spokesperson for Prime Minister Gordon Brown said he "believes that this strike is in no one's interest and will cause unacceptable inconvenience to passengers. He urges the strike be called off immediately" and the two sides return to bargaining.
In addition to the three-day strike beginning Saturday, Unite has decided to strike for four more days beginning March 27. Unite represents 95 percent of BA's 15,000 cabin crew members, but not all of them plan to strike.
The airline has unveiled an ambitious contingency plan to get as many passengers as possible to their destinations. Walsh said he hopes that by leasing aircraft and using replacement workers, BA will be able to deliver about two-thirds of its customers to their planned destinations during the strikes.
In a full-page ad in British newspapers Friday, Walsh said a "significant number" of cabin crews don't support the strike and will continue to work, supported by volunteers from across the airline.
The airline said it has also made agreements with more than 60 other carriers to rebook customers free of charge if their British Airways flights are canceled during the strike period.
But in a posting on its Web site, Unite called the schedule "an accomplished work of fantasy."
The industrial action is over planned changes to the way cabin crews operate, which British Airways says will save the carrier more than 60 million pounds ($90 million) a year.
Unite has said the plans call for working hours to be extended and crew staffing levels to be cut, changes that it has said will damage customer service and the BA brand.
"Unite believes the new contractual changes are an attempt to force staff to pay the price for management failings with the company wringing more and more out of fewer and fewer staff who will be paid less," the union said in a posting on its Web site. A cabin crew member's starting salary is 11,000 pounds ($16,500), Unite said.
Unite said that BA management submitted a formal offer to the union last week, but the offer failed to address union concerns about crew numbers and service delivery. That prompted Unite officials to announce the strike dates. BA then rescinded its offer. British Airways submitted a new offer Friday, but Woodley said it reduced the amount of pay that had been in last week's offer.
A sticking point in negotiations was reportedly how BA could be compensated for the 27 million pound ($40.5 million) loss it had already incurred through canceled tickets before the talks broke down.
Walsh said he told Unite that the expense must be recovered, so the financial value of Friday's offer was "not as attractive" as last week's. The new offer, however, would have secured long-term pay protection for all existing crew, "new opportunities" for BA crew at London's Gatwick airport, and modernization of its industrial relations, he said.
Any BA workers who go on strike now risk losing permanently their travel perks, such as free and heavily discounted travel.
"We said to them that we will not continue to provide valuable perks and benefits to people who seek to inflict serious and ongoing damage to our business," Walsh said. "It wasn't a threat. When we said that those traveling concessions will be withdrawn, that's exactly what we meant, and that's exactly what will happen."
Unite said BA cabin crews offered changes to pay and work practices that would have saved the company more than 100 million pounds ($150 million), but that their offer was rejected.
The airline's management said the proposed changes would have saved the airline less money than management's planned changes.
CNN's Richard Quest contributed to this report.