A strike by ground workers at Frankfurt airport in Germany will be extended through to the middle of the week, union officials have said.
The announcement came as another 231 flights, primarily operated by national carrier Lufthansa, were cancelled on Monday.
Representatives of the air traffic controllers union GdF said the strike will last until 4am on Wednesday.
In their demand for better pay, some 200 ground workers went on strike last Thursday and Friday. Though hundreds of flights were interrupted, most air traffic continued.
The majority of the cancellations were flights operated by Lufthansa to destinations within Europe.
Lufthansa said it called off about 100 round trips, or 200 flights, on Monday and expected that number to fall to 80 round trips on Tuesday. Passengers are being offered refunds or the opportunity to rebook free of charge for flights cancelled by the strike, the airline said.
Mike Peter Schweitzer, a spokesman for airport operator Fraport AG, said that "from our side we remain ready to talk with GdF but we are waiting for willingness to compromise on their side".
The GdF union, which also represents ground workers, has been locked in a pay dispute with Fraport AG for months. The strike came after the company rejected the result of an arbitration panel as excessive.