Uber has launched its appeal against Transport for London's decision to deny it a new operating licence in the capital.
The ride hailing app filed documents at Westminster Magistrates' Court opposing the ruling.
Uber was required to begin its appeal by Friday or it would not be allowed to continue operating in London.
Transport for London (TfL) refused to renew the firm's licence last month on the grounds of "public safety and security implications".
An Uber spokesman said: "While we have today filed our appeal so that Londoners can continue using our app, we hope to continue having constructive discussions with Transport for London.
"As our new CEO has said, we are determined to make things right."
Uber's new chief executive Dara Khosrowshahi met transport commissioner Mike Brown last week to discuss the firm's future in the capital.
The talks were described by both sides as "constructive".
TfL has a number of concerns about Uber, including its approach to reporting serious criminal offences, how drivers' medical certificates are obtained, how criminal record checks are carried out, and its use of technology which allegedly helps it to evade law enforcement officials.
The app enables users to book cars using their smartphones and is available in more than 40 towns and cities across the UK.
Some 3.5 million passengers and 40,000 drivers use the service in London, according to Uber.
Mr Khosrowshahi took over at Uber in August after predecessor Travis Kalanick resigned following a series of scandals.
The new boss has apologised for "the mistakes we've made" and accepted that the company had "got things wrong".
Uber will challenge the licence decision "with the knowledge that we must also change", he said.
More than 850,000 people have signed an online petition launched by Uber, urging TfL to reverse its ruling.