Hundreds of thousands of people have signed a petition calling for Transport for London to reverse its decision not to renew Uber's licence.
On Friday, the regulator said Uber was not "fit and proper" to hold a London private hire operator licence on the grounds of "public safety and security implications".
More than 400,000 names have since been added to Uber's petition on Change.org.
The ride-hailing app firm says it will appeal against TfL's decision.
The petition, started by Uber London, says: "If this decision stands, it will put more than 40,000 licensed drivers out of work and deprive millions of Londoners of a convenient and affordable form of transport."
TfL's concerns include Uber's approach to carrying out background checks on drivers and reporting serious criminal offences.
Uber's licence is due to expire on 30 September.
It has 21 days to appeal against TfL's decision and can continue to operate while any appeals are ongoing.
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Hundreds of thousands sign petition over Uber London licence loss - BBC News