Uber Technologies has lost a crucial battle in its attempt to hold onto its London licence after a U.K. tribunal denied its appeal in case involving workers' rights.

The ride-sharing company was told last year that it had to treat its drivers as paid employees who would be entitled to minimum wage and holiday pay benefits as opposed to individually contracted partners. The company appealed the ruling to the central London Employment Appeal Tribunal but was denied its plea Friday.

"This landmark decision is a yet more vindication of GMB's campaign to ensure drivers are given the rights they are entitled to - and that the public, drivers and passengers are kept safe," said Maria Ludkin, the legal director for GMB, a U.K. trade union. "GMB is delighted the EAT made the correct decision to uphold the original employment tribunal ruling. Uber must now face up to its responsibilities and give its workers the rights to which they are entitled."

"GMB urges the company not to waste everyone's time and money dragging their lost cause to the Supreme Court," she added.

The decision casts a major doubt over the fate of its London licence, which was essentially revoked by Transport for London authorities in September amid concerns over the vetting of drivers and the alleged use of software that would evade government monitoring of vehicles. 

Uber London filed a formal appeal against the city's decision in Westminster Magistrates' Court in central London and is expected to be heard on December 11, although the ultimate fate of Uber's operating license in the British capital may not be known for several months.

The appeal process follows a personal attempt by Uber CEO Dara Khosrowshahi to broker a deal with London's Mayor, Sadiq Khan, who has ultimate authority over TfL and has repeatedly backed its decision and put him at odds with Britain's Prime Minister, Theresa May, who called TfL's decision "disproportionate".

"Yes there are safety concerns and issues for Uber to address, but what I want to see is a level playing field between the private firms and our wonderful London taxis," May said last month. "At a stroke of a pen, what the Mayor has done is risked 40,000 jobs."

Khan had stepped into the escalating controversy after between transport officials and Khosrowshahi after Uber published an open letter to "Londoners" that accepted the company's need for cultural and commercial change.

"I welcome the apology from Dara Khosrowshahi ... Obviously I am pleased that he has acknowledged the issues that Uber faces in London," Khan said. "Even though there is a legal process in place, I have asked (Transport for London) to make themselves available to meet with him."

Uber's London business has proven controversial on a number of levels, including its use of a Netherlands-based sister company to avoid paying a 20% value-add-tax on rides booked by customers in Britain, a technique that one U.K. lawyer, who is bringing a case against the firm, has cost taxpayers nearly £1 billion.

Londoners, too, are divided on the Uber issue, with some using the #boycottblackcabs to express support while accusing TfL of "shocking protectionism" as the decision will clearly reduce the threat to London's traditional taxis, which it also licenses.

There are around 85,000 of London's iconic Black Cabs in the capital, according to the most recent U.K. government statistics, but they are among the most expensive in the world.

Carspring.co.uk, which calls itself Europe's first truly online used car dealership and is registered by the U.K.'s Financial Conduct Authority, says the average price for a 3 kilometre (1.86 mile) journey in a Black Cab is $12.35, including initial fares. That's nearly twice the price of a similar journey in New York ($7.85) and Chicago ($7.90).

Uber's London cars have a minimum fare of £14 ($18.99) but the company claims its per mile average is $4.80 - around a third less than the London Black Cab average.

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