Strikes by air traffic controllers have begun to disrupt travel throughout Europe as unions participate in two days of walkouts to protest against planned cost cuts and reforms.
The move was prompted by the EU's Single European Sky initiative, which seeks to centralize the continent's airspace and reduce congestion and inefficiencies costing airlines an estimated 5 billion euros ($6.8 billion) annually.
Traffic controllers are protesting against planned changes to rules governing European airspace. The networks handle some 9 million flights each year in a region with about 440 airports.
Air traffic controllers "are suffering from a performance scheme dominated by a continuing cost reduction and in which safety is not considered to be the first priority," Francois Ballestero, political secretary at the European Transport Workers' Federation, said in a statement. "We refuse cuts in staff."
Airlines are advising customers to check the status of their flights before traveling to airports and to prepare for potential delays.
The European Parliament is due to vote on the Single European Sky initiative on Thursday January 30.