(Reuters) - Commuters faced a day of traffic chaos in London, Berlin, Paris and Madrid on Wednesday as taxi drivers mounted one of the biggest protests against Uber, a U.S. car service which allows people to summon rides at the touch of a button.

Paris commuters faced gridlock getting into the city on Wednesday morning when taxis slowed traffic on major arteries into the center. In London, up to 12,000 taxi drivers plan to tie up the streets around Trafalgar Square, just a stone's throw from Prime Minister David Cameron's official residence, from 2 p.m. (1300 GMT).

Taxi drivers across Europe say applications of companies like San Francisco-based Uber Technologies Inc. are breaking local taxi rules across the European Union and threatening their livelihoods.

Uber, valued last week at $18.2 billion just four years since its 2010 launch and backed by investors such as Goldman Sachs and Google., contends its smartphone application complies with local regulations and that they are being targeted because of their success in winning customers.

"They're killing us off, starving us out," said Mick Fitz, who has been driving a London black taxi for years. He and other black cab drivers allege Uber's technology is effectively a taximeter and thus contravenes a 1998 British law reserving the right to use a meter for licensed black taxis.

"With their taximeter, their apps that they use, their technology, those are taximeters basically, which by law only we are allowed to use," Fitz told Reuters.

Uber has touched a raw nerve in Europe by bringing home the dangers of technological advances to one of the world's most visible trades.

A variety of apps for summoning taxis have threatened the traditional taxi model in European cities such as London where strict rules govern which cars can stop on the street to pick up hailing customers and which cars have to be pre-booked.

Uber has expanded rapidly since it was launched by two U.S. technology entrepreneurs, Travis Kalanick and Garrett Camp, and now operates in 128 cities across 37 countries.

"What you are seeing today is an industry that has not faced competition for decades. Now finally we are seeing competition from companies such as Uber which is bringing choice to customers," Uber's Regional General Manager for Western Europe, Pierre-Dimitri Gore-Coty, told Reuters.

UBER JAM?

Uber Chief Executive Officer Kalanick last week announced $1.2 billion in new funding, valuing the company at $18.2 billion, one of the highest valuations ever for a Silicon Valley startup.

But it has faced a series of hurdles from the beaches of Miami to the piazzas of Rome.

Ordinances keep it out of cities such as Las Vegas and Miami while in Chicago, San Francisco and Washington, D.C., Uber and similar companies have faced lawsuits from taxi companies hoping to keep the new competition out.

In France, taxi drivers who have been on the warpath in recent months over mounting competition from private hire car firms kicked off their Wednesday protest by teaming up in large numbers to slow traffic to snail pace on major motorway access routes into the capital.

Adding to the gridlock, a strike at the SNCF state railway company over planned reforms reduced high-speed TGV and Intercity services by as much as 50 percent, while international rail links were also reduced by about 30 percent.

About 1,000 Berlin taxi drivers were expected to protest against taxi-fetching app companies, including Uber, between noon and 2 p.m. (1000-1200 GMT), congesting roads between the Olympic Stadium and Tegel Airport, Berlin Central Station and Südkreuz Station, according to city police.

Taxis were also striking in Madrid and Barcelona. The two biggest taxi unions in Madrid, who represent around 90 percent of cabs in the capital, have called for a 24-hour strike from 6 in the morning. The Ministry of Public Works has warned that companies or individuals offering Uber-type services faced fines of up to 6,000 euros, while users could be fined up to 600 euros. The ministry has not specifically named Uber, which is operating in Barcelona but not Madrid.

(Reporting by Sonya Dowsett, Lisa Jucca, Paul Day; Editing by Sonya Hepinstall)