WASHINGTON (Reuters) – A group representing major U.S. airlines “strongly urged” the Federal Aviation Administration to extend a proposed deadline to June 2024 to retrofit airplane altimeters to ensure they are not susceptible to 5G wireless interference.

Airlines for America, which represents American Airlines (NASDAQ:), Delta Air Lines (NYSE:), United Airlines and others also asked the FAA to revise a proposed 5G safety directive “to reflect technical realities and the continued safe operation of many aircraft.” The group warned a “material number of aircraft” in U.S. fleets will not be modified by July and without changes it could “severely limit operations.”