Colorado authorities have issued an $8.9 million fine against Uber for authorizing drivers who had prior disqualifying criminal or vehicle-related offenses.

According to the Colorado Public Utilities Commission, Uber allowed 57 drivers over the last 18 months to drive who should not have been permitted to drive for the company.

The agency wrote in a Monday statement that its staff "launched an investigation earlier this year after a referral from the Vail Police Department about an Uber driver accused of assaulting a passenger."

The PUC then cross-checked Uber's provided records with state criminal and court records.

"PUC staff found that Uber allowed individuals to drive with previous felony convictions, major moving violations (DUI, DWI, reckless driving, driving under restraint), and numerous instances of individuals driving with suspended, revoked or cancelled driver’s licenses," the agency continued.

Following its investigation, the PUC found 12 Uber drivers had felony convictions, and one even had escaped from prison and nevertheless was allowed to drive with Uber.

According to the Denver Post, the PUC ran a similar check on Lyft drivers and found no such violations.

“We recently discovered a process error that was inconsistent with Colorado’s ridesharing regulations and proactively notified the Colorado Public Utilities Commission (CPUC)," Uber said in a statement provided by Stephanie Sedlak, a spokeswoman.

"This error affected a small number of drivers and we immediately took corrective action. 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.”