London's transit authority has refused to renew Uber's operating license over concerns about impostor drivers.
The ride-hailing company vowed to appeal the decision as it struggles to secure its future in the British capital.
It's the latest chapter in Uber's rocky history with London transport officials, who have subjected the San Francisco-based tech company to ever tighter scrutiny over concerns about passenger safety and security.
"About two years ago, the City of London told Uber that it needed to be more forthcoming in sharing data and particularly concerns about public safety with the background on the drivers," said Jason Henderson, a transportation professor at San Francisco State University.
"Now in the follow up investigation of how they've addressed the city's demands, the city has concluded that they have not," he said.
Uber has 21 days to file an appeal, which it said it would do.
It can continue operating during the appeals process.
Transport for London cited several breaches that placed passengers and their safety at risk in its decision not to extend Uber's license.
Among other things, regulators said unauthorised drivers carried out thousands of rides.
The denial in a lucrative European market is a big setback for Uber as it struggles to turn a profit.
In the US, safety advocates have criticised Uber for conducting less thorough background checks on drivers than traditional taxi companies, which generally check drivers' fingerprints against databases.