A strike by ground workers at Frankfurt airport will be extended through early Wednesday after leading to the cancellation of 231 flights on Monday, union officials said. Representatives of the air traffic controllers’ union GdF said their strike will last through 5 a.m. (0400 GMT) on Wednesday. In their demand for better pay, some 200 ground workers went on strike on Thursday and Friday, interrupting hundreds of flights, although most traffic continued. The majority of the canclelations were flights operated by Lufthansa to destinations within Europe. The airline has been scratching flights ahead of time and listing them on www.lufthansa.com to ease operations. 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 canceled by the strike, the airline said. A spokesman for airport operator Fraport AG, Mike Peter Schweitzer, said the cancellations come out of 1,250 flights scheduled. Schweitzer said that “from our side we remain ready to talk with GdF but we are waiting for willingness to compromise on their side.” No talks are scheduled, he said. 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.