The Federal Aviation Administration said Friday that United also failed to use a proper method for random selection of flight-crew members for testing.
The FAA said it had already warned United twice that the airline’s random selection process wasn’t scientifically valid because all employees didn’t have the same chance of being picked.
The airline, owned by United Continental Holdings Inc., has 30 days to respond to the charges.
“Safety is United’s top priority,” said spokesman Mike Trevino. “We are reviewing the letter and will cooperate fully with the FAA to resolve their concerns.”
Federal rules require pre-employment drug and alcohol screening and random testing of current employees in safety-sensitive jobs in the transportation industry.