Transport for London, the UK capital’s regulator of public transportation, has decided to not renew Uber’s license to operate in the city, which expires on September 30.

This marks a huge blow to the taxi service and its 40,000 London-based drivers, who account for a third of the private hired vehicles in the city.

Uber says that they will challenge the decision and continue to operate until their appeal processes have been exhausted.

TfL said in a statement that Uber London is not fit and proper to hold a private hire operator license. “Uber’s approach and conduct demonstrate a lack of corporate responsibility in relation to a number of issues which have potential public safety and security implications,” the statement said.

TfL also accused Uber of using a software called Greyball that can be used for blocking regulators from gaining full access to their app and criticized their approach to reporting serious offenses and background checks on drivers.

“Transport for London and the Mayor have caved in to a small number of people who want to restrict consumer choice,” said Tom Elvidge, Uber’s general manager in London. “We intend to immediately challenge this in the courts.”