A Lufthansa aircraft passes along the air traffic control tower at Berlin’s Tegel airport, August 3, 2011. A German union called on air traffic controllers to strike for six hours on Thursday August 4, 2011 to push for higher wages, threatening flight delays and cancellations during the summer holiday season. The union said up to 2,500 flights could be affected as it rejected the latest offer from German air traffic authority DFS as „not negotiable”. REUTERS/Fabrizio Bensch (GERMANY – Tags: TRANSPORT CITYSCAPE EMPLOYMENT BUSINESS)