Uber has come under fire in the past for not being stringent enough when it comes to carrying out background checks on potential drivers. The company says it has improved the process in recent times, but a Colorado regulatory agency disagrees: the ride-hailing firm has been hit with an $8.9 million fine for allowing people with felony convictions and motor vehicle offenses to become drivers.

The Colorado Public Utilities Commission (PUC) said its probe found 57 drivers "who should not have been permitted to drive for the company." They include 12 drivers with felony convictions, 17 drivers with major moving-vehicle violations, and three had interlock driver's licenses, which is required after a recent drunken driving conviction.

Uber has been fined $2500 for each day one of the disqualified drivers was allowed to work, giving the company a total bill of $8.9 million. The company has ten days to pay 50 percent of the fine or request a hearing to contest it.

"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," said PUC Director Doug Dean in a statement. "These actions put the safety of passengers in extreme jeopardy."

"PUC staff was able to find felony convictions that the company's background checks failed to find, demonstrating that the company's background checks are inadequate," Dean said. "In other cases, we could not confirm criminal background checks were even conducted by Uber."

Uber said it had discovered a "process error" in its background check system. The firm claims it was working to correct the issue and had "proactively notified" the PUC.

"This error affected a small number of drivers and we immediately took corrective action," a spokesperson said. "Per Uber safety policies and Colorado state regulations, drivers with access to the Uber app must undergo a nationally accredited third-party background screening. We will continue to work closely with the CPUC to enable access to safe, reliable transportation options for all Coloradans."

Uber uses a San Francisco startup called Checkr to research drivers' histories. Most taxi companies use Live Scan providers, which involves the DOJ checking fingerprints for any criminal records.

One Uber driver discovered by the PUC was a "habitual offender" who had previously escaped from a correctional facility. He started working for Uber after being released from prison.