Uber has lost its attempt to prevent its drivers being forced to take English language tests.
The ride-hailing app went to court after Transport for London (TfL) said that drivers should have to prove their ability to communicate in English.
Uber argued that the standard of reading and writing required by the test was too high.
The US firm said the test was "unfair and disproportionate" and it would appeal against the court's decision.
The ruling will also apply to all minicab firms in London.
"TfL are entitled to require private hire drivers to demonstrate English language compliance," said Judge John Mitting as he rejected Uber's claim.
Tom de la Mare QC, for Uber and the drivers, told the judge that the language requirement would result in 70,000 applicants failing to obtain a licence over three years.
The proposals would have a disproportionate impact on drivers from countries where English was not generally spoken and give rise to "indirect discrimination on grounds of race and nationality".
TfL argued that the requirements were vital to ensure passenger safety and to raise standards.
Sadiq Khan, the Mayor of London, said: "Drivers being able to speak English and understand information from passengers and licensing requirements is a vital part of ensuring passengers get the high standard of service they need and deserve.
"TfL will of course look at the High Court judgment in detail to ensure all our policies fully comply."
Sam Dumitriu, head of projects at the Adam Smith Institute, a conservative think tank, criticised the ruling.
"These tests are not only expensive but excessive, and will do little to improve public safety. We've already seen London taxi drivers of 20 years or more struggling with essay questions about the Aurora Borealis and snowboarding, do we need them to have read Shakespeare too?" he said.
"There's clearly no public interest here, only the interests of the vocal Black Cab Lobby. Sadiq Khan should listen to drivers and scrap them."
Uber said the judge ruled in its favour on three other points, including not having to open a UK-based call centre.