Lufthansa, which accounts for around half of the airport’s average daily movements of 1,300, said it was canceling around 140 flights.
The latest walkouts began on Sunday at 2000 GMT and are due to run until 0400 GMT on Thursday.
Each day of strikes is costing Fraport around 1 million euros ($1.4 million) in lost revenue. Lufthansa said last week the first four days of strikes had cost it a high double-digit million euros amount, but has declined to provide a new estimate since.
The GdF union is calling for higher pay and shorter hours for around 190 staff who work on the airport apron. Fraport says the demands, which would equate to pay increases of between 50 and 70 percent, are unreasonable.
The walkouts by staff representing just 1 percent of Fraport’s workforce have also resulted in calls for changes to Germany’s labor laws to prevent such small groups of striking workers from exercising such pressure.
“A mini-union cannot be allowed to blackmail a company in this fashion,” CDU/CSU politician Michael Fuchs said last week.
Fraport’s own staff council has distanced itself from the striking workers, saying they were not acting in the best interests of the workforce as a whole.
Ver.di, one of Germany’s largest trade unions, said on Sunday that if the GdF succeeded in its demands, it would make similar requests for other groups of workers at the airport.
A Fraport spokesman said on Monday: “This validates Fraport’s view that there shouldn’t be such big differences in pay for similar roles within the group.”
One attempt at mediation has already failed, with Fraport rejecting the proposal, saying that in some places it went above what the union had requested. Latest talks broke down on Friday, with the GdF saying Fraport had made a lower offer than before the strikes.
“Nothing has changed since last week, when Fraport made this ‘ominous’ offer,” a GdF spokesman told Reuters TV. “We are ready to talk and we will respond if Fraport comes to us.”
A Fraport spokesman said the group was waiting for the GdF to recognize it had made a good offer and to end the strikes.
“They have already played their trump card, and we have shown that we can cope well on strike days,” he said.
The number of flights canceled since the walkouts began on Feb. 16 is around 1,400, including Monday’s expected cancelations.
Shares in Fraport and Lufthansa fell on Monday, with Fraport down 1.2 percent and Lufthansa, also burdened by high oil prices, down 3.6 percent.
