Democrats are raising concerns about safety after the Trump administration began firing several hundred Federal Aviation Administration employees amid a series of plane crashes and other air-related incidents in recent weeks.

Several hundred probationary workers at the FAA received word they had been fired in late-night emails on Friday, according to Dave Spero, president of the Professional Aviation Safety Specialists union. Some of the affected personnel include those hired for FAA radar, landing, and navigational aid maintenance, according to reporting from the Associated Press.