Colorado regulators on Monday fined Uber $8.9 million, saying the ride-services company allowed 57 people to drive for it although they lacked valid driver's licenses or had committed other offences that would have disqualified them.
The Colorado Public Utilities Commission said its probe found violations that included 12 drivers with felony convictions, 17 drivers with major moving-vehicle violations and three drivers with a type of driver's license required after recent drunk-driving convictions.
"We have determined that Uber had background check information that should have disqualified these drivers under the law, but they were allowed to drive anyway," Doug Dean, the commission's director, said in a statement.
"This error affected a small number of drivers and we immediately took corrective action," it said.
Uber has had a difficult year in the face of a federal probe into whether it broke bribery laws, allegations of sexual harassment, and other issues that led the company to bring in a new chief executive and take steps to improve its corporate culture.
Uber has about 600,000 drivers across the United States.