Transport for London is inviting the High Court to rule whether smartphone taxi-booking app Uber is breaking the law.
The Licenced Taxi Drivers Association (LTDA) claims the app is equivalent to using a taximeter, which private vehicles are prohibited from using.
Uber uses GPS technology to allow users to hail private cabs from their location and is available in 115 cities.
Following the High Court referral the LTDA are launching private prosecutions against six minicab drivers who use Uber.
Taxi cab union members are also planning a mass protest on June 11 in Parliament Square, Trafalgar Square and along Whitehall by parking up and causing traffic chaos.
It follows a protest earlier this month when drivers brought traffic to a stand still outside the Shard.
Steve McNamara, LTDA general secretary, said: “We think it is crystal clear Uber are breaking the Private Hire Act - a buffon could have seen what it meant.”
TfL said the rapid pace of smart phone technology requires clarity and a decision should be made by a judge.
Leon Daniels, TfL’s managing director of surface transport, said: “On the issue of taximeters, the law is unclear and we have taken a provisional view.
“We will be asking the High Court to provide a binding ruling. This is the sensible approach, and we hope that London's taxi drivers and private hire drivers and operators will work with us to bring clarity on this issue."
Uber's London manager, Jo Bertram, told the BBC: "We very much welcome TfL's announcement today bringing clarity and confirming that TfL and Uber fully share the vision that technology should be a key driver in changing the way people are moving around their city, improving the experience for both riders as well as drivers."
