Lufthansa flight attendants escalated their bitter pay dispute by going out on strike at three German airports leading to the cancellation of around 350 flights.
It includes the two biggest, Frankfurt and Munich, in a showdown with an airline determined to bring down costs.
Most of the cancelled services were on short and medium haul routes.
However, about a third of intercontinental flights, including services to and from Los Angeles, Houston, Chicago, Beijing and Mexico City, were also cancelled.
Berlin-based members of the flight attendants' UFO union walked off the job for eight hours starting at 3am GMT at the capital's Tegel airport.
Their counterparts at Frankfurt, Germany's busiest airport and Lufthansa's main hub, followed for eight hours starting at 4am.
UFO then hit Germany's second-busiest airport, Munich, with a third walkout, for 11 hours, starting at 11am.
The union opened its strike campaign last Friday with an eight-hour walkout in Frankfurt and warned of more to come if Lufthansa didn't give ground.
It has given only a few hours' notice of where and when it plans to strike.
Strike costs mount for Lufthansa
Juergen Pieper, an analyst with Bankhaus Metzler, estimated the airline is losing around €3m to €5m per day on the strike.
"It is not yet a big deal, but it would be a different matter if it went on for days with the entire business shut down," Pieper said, estimating a complete grounding would cost Lufthansa €10m per day. "Then there would certainly be an effect on quarterly earnings."
UFO is seeking a 5% pay raise for the airline's more than 18,000 cabin crew workers after they did without increases in recent years. Lufthansa has said it is offering a 3.5% raise, and is calling for a slight increase in working hours.
The union objects to what it says would be only gradual increases and lower wages for new employees.
The airline and the union also have been at odds over issues such as the possibility of Lufthansa transferring flight attendants to its partner budget airlines with cheaper contracts as part of a cost-saving program, though the walkouts are focused squarely on the pay issue.
"I have the impression both parties want to take it out on the back of the passengers to show their power, and it's a shame, because it is not our fault if employer and employees cannot agree," Olaf Terbeznik, a 38-year-old IT project manager from Berlin, said at the capital's Tegel airport.
Close competition flying in from the east
Lufthansa is trying to cut costs amid tough competition from budget carriers in Europe and from aggressively expanding government-owned Gulf airlines. Their rise has hurt traditional big airlines such as Lufthansa.
The airline blamed high fuel costs and new taxes on air travel in Germany and Austria for a 24% decline in second-quarter earnings compared with a year earlier to €229m.
Lufthansa announced in May that it will shed 3,500 office jobs over the coming years to cut costs and boost lagging profits.
The cuts are part of a cost-reduction program that started at the beginning of the year and aims to improve the company's operating profit by €1.5 billion compared to 2011 by the end of 2014.
"They have strong finances and a good brand, but the current management is ambitious to achieve more favourable costs and become more profitable," Pieper said. "If they want to be profitable, they have to lower costs."
Both UFO, one of several single-profession unions in Germany that tend to be more militant than the country's traditional large umbrella unions and have caused disruption over recent years, and the airline appear in uncompromising mood.
The chairman of Lufthansa's board of directors, Juergen Weber, was quoted last month as telling the weekly Die Zeit: "It is better to let it come to a big bang before the company catapults itself out of competition."
Lufthansa spokesman Klaus Walther said that "it is time for basic pay to be improved, but we must also (adapt) to changed conditions."
Things have changed over the past five to 10 years, Walther told ZDF television. "The competition situation is completely different and the economic situation is completely different too."
Airlines such as Lufthansa generate a good share of their business by carrying partner airlines' passengers to onward destinations. However, three big government-owned Gulf carriers, Emirates, Qatar Airways and Etihad Airways, have all expanded aggressively, particularly in Europe, to eat in other airlines' long-haul traffic.
So rather than transferring in Germany with Lufthansa, passengers from North America or Europe heading to Asia, Africa and Australia are increasingly transiting through the Gulf's gleaming airports.
The Gulf's fast-growing fleets are filled with some of the industry's newest planes, and usually boast generous in-flight meals and entertainment.
Dubai-based Emirates has grown into the world's largest carrier if measured in terms of international passenger traffic. It last fiscal year pulled in $629 million in profit despite a big jump in fuel costs.
Abu Dhabi-based Etihad, which only started operations in 2003, posted its first annual profit of $14 million last year. Qatar Airways doesn't disclose its finances.
All three carriers insist they operate on purely commercial terms and do not receive perks such as discounted jet fuel. None of them has a unionized work force, however, so they do not have to contend with strikes.
Etihad late last year when it bought nearly 30% of Germany's second-biggest carrier, Air Berlin PLC. It has since amassed stakes in three additional carriers and partnered with others elsewhere.
