Lufthansa flight attendants have walked out on strike at 5:00 am local Berlin time (10:00 pm EST), making good on their threat over a 13-month wage dispute with the airline. The airline has not officially announced how many flights have been affected by the strike but some reports say as much as 20% of flight will be delayed or canceled.

The union that represents the flight attendants, Unabhaengige Flugbegleiter Organisation, (UFO) said in a statement that “The strike will take place in the location where the responsibility for the current Lufthansa disaster began,” but would not give information on how many were participating or other details.

Lufthansa, based in Cologne, Germany, implemented a cost savings program called SCORE, and flight attendants are protesting different wage scales for different groups of workers. About 19,400 workers are affected by the wage dispute.

The union, UFO, is seeking wage back pay starting in 2012. Union head Nicoley Baublies said the airline’s offered a pay raise amounting to 1.5% while the airline says it offered 3.5% over time.

Also at odds is the union’s complaint that the airline demands flight attendants based at its Berlin hub work 9% more hours than employees at other bases.

A walkout “will have a massive impact” on earnings, though the airline needs to stick to its stance to restore profitability, Peter Oppitzhauser, a Zurich-based analyst at Credit Agricole with an outperform recommendation on Lufthansa stock, said by phone Aug. 28.

81% of workers voted for the strike on a vote that was held August 8.

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