Transport authorities in London have refused to renew Uber's business license, putting the future of up to 45,000 London drivers at risk.
The Transport for London (TfL) says Uber's system has changed to allow unauthorised drivers to upload their photos to other driver's accounts, which means they can pick up passengers just like a reserved driver.
As a result, it considered Uber "not right at the moment."
Although Uber immediately said it would appeal, the process could include court proceedings that could last months.
However, the company has 21 days to file an appeal, and the company can operate during this period despite the permission being revoked.
TfL said, "The company's failure mode has been identified, including several violations of regulations that put passengers and their safety at risk."