The U.S. aviation industry on Wednesday urged Congress to approve “robust emergency funding” for air traffic control technology and staffing.

Three weeks after a deadly midair collision near Washington, D.C., marked the worst air disaster in the U.S. since 2001, groups representing industry heavyweights like Boeing, major U.S. airlines, private aviation and a host of labor unions wrote to lawmakers calling for urgent funding and improvements to U.S. airspace.

They also said the Federal Aviation Administration should be exempt from government shutdowns “to ensure a predictable funding stream to ensure continued safety and air traffic control personnel hiring and training.”

A 2019 government shutdown left federal workers without pay for several weeks, including air traffic controllers and airport screeners. That shutdown ended hours after staffing shortages snarled flights at several major U.S. airports.