Uber - which has clashed with local and national regulators across Europe since its launch on the continent six years ago - has long claimed it is simply a digital app which which helps to connect drivers and customers.
In a surprisingly quick turn of events, the court has decided that Uber is, in fact, a taxi company, and should be regulated as such.
Uber released a statement following the court's announcement saying, more or less, that it didn't know what all the fuss was about as it already operated under transportation law in Europe.
But it could limit the company's ability to use drivers who do not have professional licenses - a service now offered in only a few European markets. In France, for example, Uber's low-priced service involving independent, unregulated drivers is banned, but Uber operates a popular ride service involving licensed drivers that competes with traditional taxis.
The case was referred to the European court of justice, which ruled: "The service provided by Uber connecting individuals with non-professional drivers is covered by services in the field of transport". The decision can not be appealed.
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In Hong Kong, legislator Charles Mok, representing the information technology sector, said he believed the ruling would give the Hong Kong government "an excuse" to block Uber's operation in the city. The company's CEO has said it's appropriate to regulate services like Uber's and that the firm wants to partner with cities where it operates.
The landmark ruling will require Uber to treat its drivers more like employees.
After the EU decision, Uber said it probably won't see its business heavily impacted as it was already working under the transportation law the court imposed on them in most European countries. Bus drivers, train drivers and a huge number of cab drivers are unionised, and expect certain terms and conditions, including at least the minimum wage, and sickness and holiday pay.
Uber has already been forced to adhere to national regulations in some European Union countries.
In September London Mayor Sadiq Khan clamped down on Uber, stripping the company of its operating license. "On the contrary, this ruling serves as a very good reference for authorities to reject Uber [if they had intended to]", he said. The ruling also comes soon after the company was stripped of its licence to operate in London and saw Travis Kalanick, its founder, resign amid an ongoing boardroom stand-off.