UBER faces having to withdraw ride hailing services in London, its busiest European market, after local regulator Transport for London pulled the company's license for private hire cabs on Friday, a move Uber said it planned to appeal.

The online ride-hailing pioneer said it still operates in 96 European cities but has largely withdrawn its UberPOP service that relied on drivers without commercial licenses after court rulings against it in many jurisdictions going back years.

Only in two cities across the region - Berlin and Athens - does Uber offer rides with officially licensed taxi drivers which allow passengers to hail UberTaxis as they pass on the street. In other cities, Uber's private hire cabs must be ordered before a journey.

UberPOP remains available in a handful of cities in the Czech Republic, Estonia, Norway, Poland and Switzerland. Uber plans in 2018 to introduce ride-sharing and other services in Finland after the country recently cleared the way for such services.

In most remaining cities, Uber offers a range of private hire services using locally licensed drivers that include its mainstream service UberX, its up-scale UberBlack cars and other niche services including UberVan, UberGreen and UberExec.

The following are key legal challenges Uber has faced in Europe since it began operating in 2012 in London and Paris.

EUROPEAN UNION

A non-binding legal opinion issued in May 2017 by a legal adviser to Europe's top court found Uber to be a transportation service, not just an online app, exposing it to further local regulation across the region.

FRANCE

A French court fined Uber 800,000 euros ($957,000) in June 2016 for running an illegal taxi service with amateur drivers and slapped smaller fines on two executives in the first such criminal case against it in Europe. Uber's licensed private hire services remain popular in Paris.

ITALY

A Rome court banned unlicensed ride-hailing services such as Uber in April this year, but the ban was short-lived after the company appealed to a higher court. Uber does not operate in Milan after a 2015 ruling against UberPOP that the smartphone app represented "unfair competition" to taxis.

DENMARK

Uber said in March it planned to withdraw from Denmark after the country passed a new taxi law that required ride-hailing services to install fare meters and meet other requirements.

HUNGARY

Uber pulled out of Hungary in 2016 after the government passed a law - in response to taxi operator protests - that would have blocked internet access to "illegal dispatcher services" like Uber's ride-hailing app.

GERMANY

A German regional court in Frankfurt in September 2014 ruled Uber drivers must have commercial licenses to operate in Germany, leading the company to pull out of operations in several German cities. It now operates only a limited set of services in Berlin and Munich.