CNN -- A four-day strike by the pilots' union of Lufthansa threatens one of the world's largest airlines and may disrupt travel on more than two dozen partner airlines on Monday.
Lufthansa and the pilot's union, Vereinigung Cockpit, are holding talks this weekend as a last ditch effort to avoid the strike. More than 4,000 pilots are expected to walk off the job at midnight Monday (6 p.m. Sunday ET) through Thursday over protracted contract negotiations centering around pay and job security.
The industrial action starts the same day that British Airways cabin staff are expected to announce the outcome of its strike vote. And on Wednesday in Greece, a mass public and private sector strike is being planned to protest the government's austerity plan.
Lufthansa has already canceled two-thirds of its scheduled flights Monday to Thursday ahead of the strike.
Company officials admitted it would have a "heavy influence" on its international operations, which includes flights to 80 countries worldwide.
In 2008, Lufthansa was the number two international carrier by passengers with 42.2 million, according to the International Air Transport Association.
The threatened walkout comes as the airline industry is digging out of the worst one-year drop-off in flights, according to IATA.
In 2009, revenues dropped nearly 15 percent worldwide after generating a record $535 billion the previous year. Passenger travel fell a record 3.5 percent and freight fell more than 10 percent, according to IATA figures.
Lufthansa officials said at a news conference Thursday it would cost the airline about $33 million a day.
Many of Lufthansa's pilots have been working without a contract since March and more than 90 percent of the union's members voted to strike, said Jorg Handwerg, a pilot and representative for the union.
The union sought a 6.4 percent pay increase. The union is also concerned with the airline's recent buying spree of small regional carriers, such as BMI and Austrian Airlines which, it says, is cannibalizing flights away from union-flown routes.
"We fly less hours and have less potential for (performance-related bonuses)," Handwerg said. "We want to have the opportunity to grow, but instead it shrinks."
In a statement, Lufthansa said: "In addition to demands on job security, however, the union also insisted on a greater say on fundamental entrepreneurial issues, equating to intervention in business management at the airline. That demand cannot be accepted."
The airline is allowing passengers to rebook flights for tickets purchased before February 18 and plans to give German domestic passengers rail vouchers.
But one Lufthansa passenger said she is having trouble reaching a compromise with the airline.
"I spent several hours on the phone with Lufthansa to try and figure out what I can do, but now I've been told that I can't even get a refund," said Ruth Winblad, who is supposed to fly Monday from Gothenburg, Sweden, to Rome, Italy.
Lufthansa is one of the largest carriers on Star Alliance, a network of 26 airlines that share ticketing and routes for international travel. Travelers on Star Alliance flights are advised to check their tickets for Lufthansa flights and contact their carrier about any potential changes, said Markus Ruediger, Star Alliance spokesman.
Star Alliance member airlines are: Adria, Air Canada, Air China, Air New Zealand, ANA, Asiana Airlines, Austrian, Blue 1, BMI, Brussels Airlines, Continental Airlines, Croatia Airlines, Egypt Air, Lot Polish Airlines, Lufthansa, Scandinavian Airlines, Shanghai Airlines, Singapore Airlines, South African Airways, Spanair, Swiss, Tap Portugal, Thai Airlines, Turkish Airlines, United Airlines and U.S. Airways.
Partner airlines are preparing for the potential strike.
"Some of our codeshare flights with Lufthansa may be affected during the period of the strike. We are in contact with Lufthansa and will be informed of the affected flights as soon as details are made available," said Nicholas Ionides, Singapore Airlines spokesman.
"Should there be customers traveling on affected Lufthansa-operated codeshare flights, they will be contacted and re-accommodated on the best next available schedule."