UberPOP has been present in Paris since 2011 and has expanded to other cities, but it also faces a legal battle in France, where the Paris appeals court is considering whether to ban it.
The service, which links drivers of private cars with potential passengers at cheaper rates than traditional cabs, became available in Marseille, Strasbourg and Nantes on Monday.
Around 80 to 100 taxi drivers protested in the western French city of Nantes in front of a hotel where Uber was organising a driver recruitment meeting.
"Our main fear is unfair competition: these people pay neither social charges, nor the right to park on the public highway," said Sebastien Leclair, head of the CPAT taxi association for the Loire-Atlantic region.
CPAT called on taxi drivers to step up action on Tuesday in Nantes, including possible moves to block traffic in and around the city.
As well as Paris, UberPOP was already available in Lyon, Bordeaux, Toulouse and Nice.
San Francisco-based Uber faces legal challenges in several European countries where licensed taxis drivers have protested.
A French court last month outlined restrictions on private chauffeured vehicle services, called VTCs, such as the one offered by Uber.
UberPOP is a more informal operation than VTCs, which use professional drivers.
Uber said UberPOP simply heralds the imminent deployment of a so-called VTC (chauffeured tourism vehicles) service in the three cities.
© Thomson Reuters 2015
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